Getting from CDG to Paris with family of 5

Some of us say nay problem.

I just took the Roissy bus from CDG to Opera (metro lines 7,8, 3) by Galleries Lafayette. So convenient , comfortableand reasonable. Cost is 11euro per person regardless of age.

The better deal is buy the Paris Visite Pass which covers 5 full days of unlimited bus, metro, RER to Versailles. I believe there is a 3 day pass too. Children have a discount fare. The worse part we lost a child's ticket; you have to hang onto everyone's little ticket for 5 days.
I have also used Air France Shuttle which drops off by Etiole next to metro lines 1,2,6.

A taxi is the cheapest option for five people. Taxi vans are fairly common and you won't have to wait long at the taxi rank.
The Visit Passes rarely pay for themselves, but you should compare the price with buying carnets of ten tickets. Staying in the 5th means you'll be very centrally located.

Thank you everyone, it sounds like the tax will work great.

The Paris Visite Pass will almost always be a very very bad idea and they are fiddly little tickets that are easy to demagnetize or lose. They are also very expensive and rarely give value. If you are there mostly between Monday and Sunday of one week get a Navigo Decouverte which is a more manageable, durable, and much cheaper product.

If you are there over a weekend and so an ND doesn't fit then buy carnet of ordinary tickets for 14.10 for adults and 7.05 for kids 4-9. Hand everyone one to start the trip and make sure every one hangs on to them (or Mom or Dad collects them and puts them in a special pocket) till the end of the trip in case you encounter a ticket inspection gauntlet (fairly common) Then once outside the designated holder throws the batch away. That way you don't mix up used tickets with new ones. But you also since you use a new ticket each time don't worry about losing a single ticket over 5 days.

Taxi will be the cheapest, especially since they've instituted (as of March 1 2016) maximum taxi fares from the airports into Paris.

From CDG to the Left Bank, where your hotel is, the maximum fare is now
55 euros
plus 4 euros for the 5th person
plus the 2.60 pick up fee

they have eliminated extra fees per bag,etc.

So for just over 60 euros--or 12 euros a person--you'll have a taxi to take you directly from the airport to your hotel, no negotiating the Roissybus and the metro, or the RER, or whatever.

You won't have to wait more than a couple of minutes for the larger-sized taxi to arrive.

http://www.aeroportsdeparis.fr/docs/default-source/passager-fichiers/acces/affiche-taxis_paris-cdg.pdf?sfvrsn=4

You won't have any problem finding the taxi stands, they're well signaled, but here is where they are at the various terminals (Porte means the door, which are are all labeled with numbers):
• terminal 1 : porte 24 au niveau arrivée
• terminal 2A : porte 6
• terminal 2C : porte 14
• terminal 2D : porte 7
• terminal 2E : porte 12 au niveau arrivée (on arrivals level)
• terminal 2F : porte 11 au niveau arrivée (on arrivals level)
• terminal 3 : sortie du hall arrivée (the only exit at arrivals hall)
• terminal 2G : porte bleue (blue door)

You've gotten great answers on the taxi issue so I'll just throw in my vote with Jane regarding the Paris Visite Pass. That one is indeed a very expensive option that's nearly impossible to get the good of. We barely got through one shared 14.10 euro carnet of ordinary tickets over our full week in the city (so much fun to walk!!!) but if you really want a transport pass - and it'll work with your timing - then Navigo Decouverte is the way to go.

The Paris Museum Pass (NOT the Paris Pass, which includes the Visite) on the other hand, was a good buy for us but like any pass, you have to do the math to see it'll work in your favor.

The 'pick up fee' is part of the 50-55 if you get the cab at a cab stand as at the airport. There can be an approach fee if you call one.

It is important to confirm the flat fare when you board the cab with the driver so he knows you know. There have been reports of some cab drivers charging 55 to the right bank or running the meter within Paris and pretending the flat fare is just to the boarder when the meter starts. Not many, but if it continues I imagine that people will stop trusting cabs.

A cab will be the best and cheapest way to the city for this family and as someone noted, there is an add on fee of 4 Euro for the 5th passenger.