Best area to stay in Paris and any advise in Paris and Lourdes

You'll be staying in two very nice areas, well located for sightseeing. Too bad about the 4th floor walk-up, but the Ile St-Louis is charming and central, a unique experience. Parc Monceau is one of my favorites too. Organize your sightseeing around your two locations if you can.

You can do without an organized tour unless you want a very customized (and expensive) experience. The Metro is an excellent way to get around, and the buses work well too (takes longer but you get to see the streets etc.). Learn enough French phrases to greet people, say please and thanks, ask simple questions, etc.

Not knowing your family, I'd still suggest splitting up for some of your time. The three older "kids" may have interests different from yours, and should be able to navigate the city on their own. The youngest might have his or her own interests and capabilities.

Besides Notre Dame, sights of particular religious interest to Christians would include Sacre Coeur, St-Sulpice, and St-Denis (a northern suburb), The Shoah Memorial and Holocaust Memorial are both very close to the Ile St-Louis.

Thank you so much Dick.
will the unique of the st Louis worth climbing the stair?
Which one is more central to transportation systems

Be careful; in France the ground floor is numbered zero, so the first floor is not the ground floor, but the floor above it. So, if your apartment is on the "fourth floor" using the French numbering system, it would be on what Americans would call the fifth floor (four flights up from ground).

Only you know how easy or hard it will be for you to climb stairs. The Ile St. Louis (not "Louise") is lovely, often tranquil (except right near the famous Berthillon ice cream shops) and very central. As a result, it's often quite expensive. Parc Monceau will be farther from sights, and you will need the Metro more (from Ile St. Louis, you will be able to walk to many sights, and if you do take the Metro the rides will be shorter). I don't know the area around Parc Monceau so I can't comment on it directly.

For advice on the rest of your trip, get Rick Steves Paris as soon as you can. The book will have all the details about how to plan your time in Paris, how to get around, places to eat, and lots of other things you didn't even think to ask. Then if you have questions the book doesn't answer, ask them here.

What a wonderful city to celebrate your 25th anniversary!

I would recommend staying at the same location in Paris the entire time you're there (couldn't tell from your posting if you planned multiple locations). Any location within the single digit arrondissements would be fine for navigating the Metro - my favorites are #1, 4, 5, 6, 8.

You don't need a tour for the Eiffel Tower, but go on their website and reserve tickets, so you don't need to stand in a long line. Otherwise, pick up the RS Pocket Tour book (has a nicer-size map), and there are plenty of recommendations that you can see as a family on your own. Don't let it be over-whelming - just pick some of your favorites. The metros are very easy to navigate. Also consider an evening cruise on the Seine. The buildings are beautiful lit up at night - very romantic.

Since you mentioned Lourdes, a few faith-related sites in Paris occur to me.

The chapel of the miraculous medal, which was the convent of St Catherine Laboure, is lovely. It's on Rue de Bac. You can get there by Metro, but bring a good map; it's a walk from the metro stop. Here's the web address:
http://www.chapellenotredamedelamedaillemiraculeuse.com/EN/a__Welcome.asp

There is also a shrine to St. Vincent DePaul nearby.

Also, if you're interested, you can spend all night in prayer and adoration at Sacre Coeur. There has been constant, 24-hour prayer since the basilica first opened. You need to make arrangements before hand, and I did it by email. They do assign you a room so you can spend some time sleeping if you'd like, and there's a very simple breakfast in the morning. However, be aware that you can't leave in the middle of the night. When they lock the church around 11 PM, you're in until it opens the next morning. The info is on their website:
http://www.sacre-coeur-montmartre.com/english/

Have a wonderful trip.

Thank you so much Harold, Jean and Sherry for your valuable tips :)

It's help us a lot.

My favorite is the Rue Cler neighborhood, near the Eiffel Tower and other important sites (Napoleon's Tomb, Rodin Museum, boat dock for the Bateaux Mouches). With the metro, you can reach any other part of the city. And most people end up walking more than they thought they'd imagine - walking time east-west across the city is about 1 1/2 hours. Our France and Paris guidebooks list our recommendations for that neighborhood and others, as well as restaurants and sightseeing details.
Yes, use the metro!
No need for a tour at the Eiffel tower, but reserve ahead at www.tour-eiffel.fr. A company called Paris Walks offers a good variety of tours, in English, and would be a nice way to initiate yourselves in your first day or two (www.paris-walks.com)
There are several direct trains from Lourdes to Toulouse every day. Google the Toulouse airport to find what options you have to get there from the city.

You might also want to check out parisgreeters. It's a great way to meet parisians and something I didn't know about when I went.

Ile St. Louis is our favorite neighborhood in all of Paris. The 5th floor is definitely worth it imo. Ile St. Louis is charming, surrounded by the river and beautiful views. It's in the very heart of Paris. I loved being so close to Notre Dame and seeing it often, early morning, day time and beautifully lit up at night. Ile St. Louis is like a little village unto itself with a grocery store that I enjoyed very much, a produce store on the corner of the main street (rue St. Louis en l'Ile) and rue des Deux Ponts that sells the best fresh squeezed OJ we've ever had (and we live in California), a post office, pharmacies, a wonderful church on the island (3/4 to the east on the main street), a nice park at the eastern end, wonderful cafes and restaurants, fun shops, and great ice cream from either Berthillon or Amarino. There are wonderful street entertainers on the pedestrian bridge from the island to the back of Notre Dame all day and at night, and at night in front of Notre Dame.

We stayed for a month in a 6th floor apt in the heat of summer and while I didn't love the climb, it was well worth it to me to stay on Ile St. Louis. Public transportation is easy from both of your apt locations.