Taxis at CDG hold up to 7 passengers (obviously that would make luggage tight and it would be sitting in people's laps -- but a van taxi for 4 should work fine for your family. Head for the official queue and do not take offers or advice from anyone who approaches you from 'need a taxi' to 'this line is for the suburbs, the Paris taxis are here' -- these people are crooks and will scam you. In some terminals there are foot prints on the floor leading you to the official queue. In any case it is well signed. Join the queue, as you get close to the head let the dispatcher know you are 4 -- with 4 fingers -- the dispatcher will put you in a large taxi. You may need to step aside for a minute till one is there or is summoned.
The cost is fixed 55 to the right bank and 65 to the left and covers 4 people and luggage; there are no added fees of any sort. Tipping is not required or common. Hand the cabbie a sheet with the address clearly printed on it including the arrondissement (the address will have a number 75XXX include that. If you want to use a credit card, hold it up before getting in and ask 'ok'? They are required to take them;sometimes the machine is magically 'broken' as they prefer cash
Oh and when you meet the cabbie, say 'bonjour' before giving him the address. No to do so is rude and tends to elicit a less pleasant response.