"can't miss" highlights of Paris are?

Ste-Chapelle isn't a cathedral rather a small beautiful chapel.
Think about what museums you want to see. D'Orsay is home to the Impressionists, a treasure.
Musee Rodin is mainly outdoors, as it is a sculpture garden. You can see "The Thinker" there. Just buy the inexpensive tickets to the outdoor portion.
Another very small and special museum is l'Orangerie in the Jardin Tuilleries. Monet's large Water Lilies are there and are mural sized. You have such a short time in Paris so these small museums would give you a taste of art without overwhelming you which the Louvre tends to do.
Your boys might enjoy seeing Napoleon's Tomb and visiting the militaey museum there, all in Les Invalides.
A river cruise on the Seine is a great idea at the beginning of your stay as most of the important sights are along the riverbanks. It will give you a good orientation.
I have never had any problem walking into Notre Dame. Perhaps the lines are for the tower?

When we were there, the line to enter Notre-Dame went very quickly. We did not go up to the towers; I believe that line takes longer. In addition to what you mention, we enjoyed walking around Luxembourg Gardens (watching children with their sail boats, older folks playing bocce ball), and also the Pantheon. That is probably not a "must do" for a short time, but it was very interesting and much less crowded. I loved the D'Orsay but my husband was not as interested in that museum (he loved the Louvre). Lots to see and do; take time to enjoy where you do go rather than run from place to place to get as many places in as possible.

The catacombs are amazing, but the lines can be hours long, even with pre-bought tickets. With the 2 1/2 days that you have, what you've listed (Louvre, Eiffel, Seine and St Chapelle) is plenty. Leave yourself some time to just explore the neighborhoods and wander into a local outdoor cafe for dinner. Montmartre is a great area to explore, wind your way up to Sacre Couer, enjoying the street musicians and little shops along the way. Or walk along the Seine after your river cruise and enjoy the beauty from another angle. The amazing crypts and grave stones at Pere Lachaise tell so many stories (Mozart, Jim Morrison, Oscar Wilde, etc.). The lines at Notre Dame can be long, but sometimes there's no line at all. Even if you just view the outside it's beautiful. You also have the statue of Charlemagne there and plenty of other visual goodies. Enjoy Paris!
Lisa

Another museum that is very nice is the Cluney . The musee de Moyan age.It is small museum but has the Lady and the unicorn tapestries. But it also has a wide rage of other items from sculptures to stained glass. Because it is small you can get up close with a lot of the exhibits. I would not try the louvre unless you take tour of the highlights.

Another thing you can do is take the water bus between major sites. Why not ask everyone what is the main thing they want to see and you may have a consensus.

The only Cathedral in Paris is Notre Dame where the lines are MUCH shorter and quicker than the lines for Ste Chapelle which partly due to its location within court buildings in Paris has very high security and a slow security line.

This is such a quick trip that the problem is not identifying but eliminating high lights. figure out what your dream of Paris is and the focus each half day around that and then add on other things in the area. I would have each family member identify their one big thing and build from there.

For me Basilica St. Denis would be a must and so different from the rest of the list, but YMMV
https://janettravels.wordpress.com/2010/10/26/confronting-mortality-at-st-denis/
It is not central but is on the metro.

Note that the Orangerie is a very small museum the major focus of which is the giant Monet Murals, so that might be a nice choice -- and it is set in the stunning Tuilleries park where you can get coffee or lunch and rent toy sailboats to sail on the fountain pool. There are also ice cream kiosks in the park.

For me a must on each trip is a walk around Notre Dame at night; one of the great sights in the world and it makes fabulous photos.

Janet - Fabulous blog post! I consider myself something of a Gothic church completest yet I knew nothing about this place. My husband has 4 days off - we may find ourselves driving to Paris tomorrow! ;)

It's funny because we were discussing St. Denis and his poor head this very evening (we're weird) in the context of a church where, bleh, the story is boring, but anyway. Cool info!

OP: I think your current plan is pretty good, go to St. Chappelle first thing in the day to avoid big crowds. I got in with a 20 minute wait first thing. Don't worry too much about Notre Dame, the line moves fast. The Louve is amazing but overwhelming - on a short schedule I'd consider skipping it (heresy) for the beautiful Musee Cluny in the Latin Quarter which is a a beautiful gothic abbey with the famous "Unicorn tapestries".

For me Paris is a city of neighborhoods and I'd focus on one or two for strolling and taking in the local culture. I like Le Marais, which is both somehow hipster, traditionally Jewish, and gay, just in a relatively small area. Montmarte is touristy but pretty. Ill-St-Louis is small and worth a quick look.

The Catacombs are super cool ( your teens will love it) but get there at opening, the lines do get ridiculous. I was there at 11am in October and we waited an hour. Multiply that in summer.

Top of my "do not miss" list are the Luxembourg Gardens. Something there for all of you... cafe, flowers, trees, tennis, basketball, chess, bocce ball, crèpe stands. Wonderful place to walk or sit and relax in the shade while still enjoying being in Paris. A picnic lunch, or pastries from a nearby bakery makes a nice break from all the sightseeing... : )

Another option would be an evening concert at Sainte Chapelle. It's usually classical music, so judge your group's interest. You can buy tickets online ahead or once you get there. When we went, they just added chairs to fit the number attending. It's actually better to sit towards the rear to see the windows.

You might also consider splitting up your family group if your interests are strong but different.
Then when you came together again (at lunch or dinner?) you would have plenty to talk about.
Do be sure to save time for walking around a neighborhood or two.
Paris has something for everyone but not everyone will necessarily enjoy the same things.
I adore Paris. Have a wonderful time!

For me the highlights are watching the sunset from the Trocadero, right across the river from the Eiffel Tower and seeing the first twinkling lights on the hour,on the Tower, the Musee,d'Orsay where the clocks amaze me and the open air food markets. Google Paris food markets and you can find a list. My faves are Grenelle, President Wilson and Monge.

Enjoy Paris.

Buy tickets online if you decide to go to the Catacombes. The lines wrap all the way around the block.
The dedicated entrance is roped off, right in front of the entrance.

Also, both stairways are the tight, corkscrew kind, not easy to navigate, and there are no landings if people want to pass you up.

have you asked the boys what they are interested in.. they should be be contributing to trip planning.. ( thats what I made my kids do.. much to my chagrin the deal was they find three sites and I take them to them.. and then they cant whine about sites I wanted to see.. my then 13 yr old "discovered " the Catacombs so I had to take him, and I am mildly claustrophobic.. lol)

All three of my kids had trips to paris one on one with us ( between ages of 11 and 14) .. and all liked the Invalids Army Museum , one son preferred the Louvre to the Orsay, but my daughter preferred the Orsay.

My daughter oohed and ahhed at St Chapelle and enjoyed a relaxing visit there, but my sons sort of went "cool" can we leave now..

All loved climbing the Towers of Notre Dame.. get in line before it opens( line for Towers is around side.. not in front)

All liked ET of course.. and going up Arc D'Triomphe and the tower of Sacre Coeur.. they seem to like climbing things.. lol exhausting.

none of us liked Pomidou. no, thats not true.. a few years ago my daughter was fascinated by an exhbit of pubic hair on a chair.. ah , modern art. The view is nice from top though.

To avoid a long line at St. Chapelle, I went to an evening concert. The place is really amazing. Try to go before dark so you can enjoy the stained glass.

Don't worry about the lines at Notre Dame. It's a security line only and it moves fairly quickly. I went once with a line and the formidable line probably ended up being a 15 minute wait. I went a second time at about 8 in the morning because there was no line and the place was quiet.

The parks are great so plan to see at least a couple, maybe Luxembourg and Tuileries.

For art, you should visit the Orangerie and Orsay in addition to the Louvre.

For shopping, go to Printemps (great view from the roof) or next door at Galleries Lafayette.

I also think you should add the Arc de Triomphe to your list, especially in the evening when you can see the city lights and the Eiffel light up at the top of the hour.

For history, everyone who was anyone was buried at St. Denis. There is also a small roman ampitheatre in town where people picnic in the seats while kids kick soccer balls on the floor, Arenes de Lutece.

Personally, I'd ask the grandparents and parents what would be the top of their wish list -- particularly since they've not been before -- and zero in on those first. Who knows if they'll get a chance to return. Next do some things you and the spouse are interested in. Then see what the boys want to do. Nothing like unhappy teenagers -- but they'll have plenty of chances to return and do their own thing..

Lots of good advice here.
Picking sites is so personal that it's hard to suggest priorities to someone you don't know. In London, one of my top "must see" sites was Harrods Department Store. I'm sure that 's not on everyone's list. My point is that it's important to emphasize your family's own interests.
I really like janet's idea of splitting days in two, with a major attraction in each half day. And I think it's a good idea to have each person pick their own "must see".
A couple of observations:
Your list has nice variety for a first time visit.
The line to enter Notre Dame can be long. We were amazed to see how long when we looked down at it from the tower (late morning). It snaked around the entire plaza in front of the Cathedral. I don't know how fast the line moves.
Arrive at the catacombs before, not at, opening time - a minimum of 1/2 hour early. We got there 10 minutes early and the line was already around the block. And the catacombs line is very slow.
You can see in these posting that opinions vary about Museums. Hard to say if you'd like the Louvre best but it may be one of those things (like Harrods) that you just have to do.
Have fun.

We were in Paris in April and our tween girls really wanted to see the catacombs but the line was impossibly long. Buy tics online or arrive before opening time. Only 45 people are allowed at one time and it takes an hour to walk through. They enjoyed climbing the tower at the Sacre Coeur --there is a charge for this now. They also liked visiting Deyrolle Taxidermy (free)--really interesting place! We arrived on a Sunday morning and first place we headed was Notre Dame--mass going on but they let people walk through and the music was very nice. We did buy Eiffel Tower tics ahead but the wait was about an hour--lots of security there.

Thanks, everyone, for your wonderful responses. These are all great ideas and I hope we can incorporate many of them. As I was told many years ago by a good friend - "Save something for next time!" And we will!
Nancy

The line to enter Notre Dame ( church not the towers) always looks very long.. but it moves steadily so its worth getting into .. there is no admission, its just a bottleneck at entrance and security.. but people dont really linger inside so the line keeps moving steadily as people circle through the church and out.. counter clockwise .

Lines for Towers of Notre Dame and Catacombs are slow .. as noted because they are capacity controlled. As last poster mentioned, get in line for Catacombs BEFORE it opens.. at least 30-45 minutes before in high season.

Also depending on ages of boys.. let them go off on their own.. they dont have to stick like glue to you if they are a reasonable age ( say 15 or more).. Parisien children walk alone and take the metro to school alone by age 10-11.. not suggesting a tourist do that.. but by age 15-16 I do suggest it.

Of course it depends on what everyone is interested in seeing, but with grandparents, teenagers and yourself, this might be varied.
Of course my #1 recommendation would be the Eiffel Tower, but you have it covered.
I think the Pompidou museum and area in front with fountains, street vendors, cafes might interest the teenagers, and from there walk into the Marais. Everyone will likely enjoy the D'Orsay, and this may be an option instead of the Louvre, which is huge (unless you really have to see the Mona Lisa) It is smaller, in a fantastic building with great art.

The Monet waterlily murals in the Orangerie are spectacular and easy to do, and the art on the lower level is impressive and it's not a very big space.

Whether you do the Louvre or not, walk from the courtyard pyramid down the Tuilleries to Place Concorde. A great stroll for young and old. Or find a chair to sit in and watch the world go by. Great place to rest.
I'd do a Seine boat cruise in nice weather, St Chapelle during day when light is good for viewing the stained glass.
Your teenagers may enjoy climbing up to top of Notre Dame, lines are long for this and requires ticket. (high climb and claustrophobic -- grandparents and you may not appreciate)
But to get into the cathedral is easy and free and even if lines out front are long, it moves pretty quickly. I always go in every time I'm in Paris.
Walk around the Islands, banks of the Seine, cross over some bridges. Find interesting cafes to hang out. Have at least one nice meal.
Cafe Constant not far from Eiffel Tower is a good place for this.
Cafe Le Nemours on Place Colette (across rue du Rivoli from the Louvre) is very good also, particularly their outdoor tables -- which you must have!