We went the first week in Sept and had a good time. It was busy but quiet as oppose to what it would have been just days before.
Stayed in the Newport Bay hotel as the mother in law paid. It all depends what you want to spend as to which way is best to do it.
If you want to save money dont buy food and drink there, however its not that bad price wise (burger type meal is about 11-13Euro, sit down meal can be 30-£35E for a set menu, to 30 euro for a main, but then do you want a full on silver service meal? Prob not but it was nice as it was included and good quality. Burgers in teh park are better than mcdonalds, however there is a mcdonalds that charges normal prices opposite the big balloon between the park gates and the hotel. Drinks again are quite a bit but just fill up on the water fountains and take whatever you like in. We were told you couldnt, you CAN! They do a bag search or xray it but its not for food and drink.
If you stay in the hotel and want a drink when the kids are asleep the best bet is to take it with you as its 7E/half litre beer or 12E for a single, wine 8E small glass.You can eat there too and the bar restaurant prices are dirt cheap in comparison but its time and you need to pay to get there unless you drive.
If you mix it with Paris, i wouldnt stay there, just hop on the train from where you stay, try stay near a station, however be prepared for a push and shove on the way back, its busy a few hrs before the fireworks end so god only knows what its like after they finish.
Depending on kids age, if they are young there isnt actually much to do other than queue for a ride go on it and repeat. There is nothing in teh way of play areas other than one naff one for them to create their own play, thats my only criticism of the place for toddlers