Lots of people come to my French blog through Google as they search for places to brunch with their kids, and I also have a hard time finding nice places. By chance, I've just found a site that lists addresses of brunch in Paris area : bruncher.com
There is a section for children. While we do not like "The Hall of Birds" in Jardin d'Acclimatation or "Café de la Jatte", there is a bunch of addresses we haven't tested yet !
Feel free to leave comments on the addresses given, they will be useful to everyone.
You may like this place we discovered recently: "The Parisian coffee," in Neuilly, Sablonville street: It is an American
restaurant with brunch on weekends. The hamburger and Caesar salad we had were perfect, we'll get there very soon to test the the brunch with the kids.
They also have 2 other restaurants inside Paris, never been there, please let me know your opinion !