Start off by going up Eiffel Tower. Get there early to avoid the long queues.
After trip to the top, head towards Trocadero, there is a traditional carousel at the foot of the Trocadero gardens. Ds2 will live it.
Then walk up the Trocadero gardens, towards Place Trocadero. Pleasant little walk, there's a little kids play park with slides etc on the left (if you have the Eiffel Tower behind you).
At the top, there's a fantastic view of Paris, down towards Eiffel, Champs de Mars, over to Invalides, the whole of Paris befor you.
On Place de Trocadero, there is a semi circle of brasserie / cafe places to eat. All with terraces outside if sunny. Most are great for eating with kids, as they have classic, brasserie fare (steak hache + frites, omelettes, croque Monsieur, spagetti bolognaise) which goes down well with kids. Our fave is Cafe Trocadero but frankly they are much if a muchness so just choose the one you fancy / one with a nice table outside with no eating. NB there is one place (Le Coq, you can't miss it, it is very red) which is best avoided as it is a very hip, very expensive lounge bar and whilst fun for a grown up dinner, too expensive for a family lunch.
Voila.