From airport to Paris

If cost is not an object then take a taxi. If it is or you want your children to have some excitement upon arriving and they can handle it, take the RER. The train ride from the airport will be pretty uneventful. The real work does not begin until you reach the metro stop that will take you to your next connection on the Metro. Most of these stops have escalators to the next station level or the street, and there is no guarantee that cars will not be crowded, but so what, 10 million people visit Paris every year so there is someone dragging a bag on nearly every metro car you enter. I take the RER each time I visit, 10 euros per person, and never regret the choice, and save a few euros along the way.

Since 4 RER tickets will run you 39 euro, a taxi or car service starts looking better.
To go by RER/metro would still involve a lot of walking, station transfers up and down stairs, many without escalators or elevators. First a walk from Terminal 1 to the CDG transit train to get to the RER station. Then a change with a lot of walking at Chatelet-Les Halles to the No 7 Metro platform to get to Place Monge, then a 500 ft walk from there to Rue Mouffetard.

The time difference is likely to be negligible either way since you will need to buy RER tickets (which necessitates a line) etc etc. And of course you are prime targets for pickpockets and petty thieves tired and with all your valuables so if you take the train in, be sure you are pickpocket proof.

With 4 people, it will cost 40 Euros for the train (children's fares are for those 9 and under). A cab will be about 60 including the 3 Euro for the 4th person. Given the convenience of door to door travel with luggage and tired jet lagged travelers, a taxi is definitely the smart move here IMHO. Go get in the official taxi queue and they will put you in a cab large enough for your group and luggage. I would never take the train with luggage with this many people.

There will always be stairs in the metro between platforms and out to the street. Even where there are elevators or escalators most stations still have some stairs and it is very common for escalators to not be working.

Take a taxi. It is 9.75 euros per person for the RER and one change to get to Metro Line 7 (the most likely Metro line to your accommodation) and that change would be Chatelet Les Halles -- a very large transit hub with a decent amount of walking. You could switch to a bus from the RER at Luxembourg instead of getting on Line 7. Or you could take the Roissy bus from CDG to Opera and walk over to Metro line 7 and take the metro from there. Mass transit = slightly less than 40 euros and hauling your luggage and having to transfer once. Taxi = most likely around 65 euros but could be up to around 85 euros. Is the convenience worth the extra cost for you and your family?

FWIW train prices go up every January 1. The cost of an adult ticket to Paris from CDG is now 10 Euro (7 for children 4-9, free for children 3 and under)

I've been to Paris several times and always take the RER train but in your situation if you have more luggage than a small carry-on each you would be much better off taking a taxi, they will take you to the hotel front door. Carrying multiple pieces of luggage through the RER & Metro would not be fun while trying to keep track of a 12 and 10 year old. You could take the Buses but I think the children will enjoy the Taxi ride once you get into Paris, I love the first time I get a view of the Effiel Tower or Arch de Triumph, or the River Seine. While your in Paris make sure the kids get to see the Versaille Pallace and plan on spending several hours in the gardens they will like it.

Another vote for a taxi! I love coming in to Paris by taxi so I can look around. To me it is just so exciting!

If you're landing at 16:20 on a week day, you're going to have to deal with a crowded RER or taxi traffic jams once you are within the Paris city limits. The RER and Metro may be extremely crowded from Gare du Nord on, or if in a taxi you'll be sitting in some traffic part of the time once within the city limits. It's just part of the trip at that time of day and may push the taxi fare a little higher.

Getting to the bottom of rue Mouffetard is not very convenient when lugging baggage. It's a few blocks from all possible metro stops, in addition to all the hauling up and down getting to the RER and changing to a metro or bus. With two kids, you should probably get a van-size taxi and enjoy the view above ground even if it's stuck in traffic at times. I've taken every possible vehicle into town from the airport, except motorcycle taxi, and have no preference of one over the other; it just depends on the circumstances.

I'm a RER type person, but have used the Paris-Shuttle, http://www.paris-shuttle.com/default.asp, in the past. So a shuttle service is another option, 64 Euros for 4 persons in a shared van or 75 Euros for a private van. The blue Super Shuttle, http://www.supershuttle.com, we see in America is also available in Paris.
Enjoy your trip.

We have used Super Shuttle here in the States. Just for fun I looked up what it would cost my husband and I to get from hotel to CDG airport and it was 27€ + 16€ (for each additional traveler) so for the OP it seems a taxi would be cheaper. I vote taxi....if it were me I would be nervous handling bags and keeping my eye on my kids all the while trying to manage train schedules and connections.

I like RER and it's as easy to use as the Metro, but in your situation I'd spring for a taxi. Won't cost much more or take much longer and a lot more comfortable and convenient, door to door. After you've settled in Paris, take the kids charging around on Metro and buses to see the sights. Enjoy the trip!

Shuttles are notoriously unreliable in Paris which does not have a shuttle culture; they are grafted on for US tourists. If they don't show, they blame you and keep your money -- 'we were there but you weren't.' If they don't have a driver, they give you the gallic shrug and you can figure out how to get to the airport; odds are they won't notify you. I would never take one TO the airport where the stakes are loss of thousands of dollars if they are unreliable. And never take one you have to pre-pay. Taxis are inexpensive -- the shuttle prices quoted above are more than I have ever paid taking a taxi to or from the airport and there is no waiting around for a taxi. If taxi fares are too high, take the RER -- you know it will get you there.

In the US when a shuttle has missed the pick up for me, which has happened twice, the company each time sprung into action and made sure I got to the airport. Once they sent a shuttle to get me and once they told me to grab a cab and they would pay for it and did. This is not what we hear when shuttles fail to materialize in Paris.

Can I ask a follow up? For OP coming from a long flight, I would get a taxi. When we got to Munich last summer, same age kids and same luggage, we thought we would take the train, but upon arrival, ended up in a taxi! Just easier!

We also will be going to Paris with same kids and same bags, arriving on a Saturday afternoon on just a short hop from Scotland. We are staying at the Novotel Les Halles so seems that is where the RER lets off for the change? If so, given our short flight and being at the correct station, should we take the RER? Kids are good with their bags, traveled all over last summer and managed their own bags on Munich and Italy trains.

But for OP after a loooong flight I do agree with taxi! :)

Thanks!!
Kim

I am not OP but we took a taxi from our hotel very close to the Ecole Militaire to CDG airport in Paris. It was 6:30am on a monday morning.....very little traffic and the fare was 61.50 euros.