We went to a giant science place Cite , loads of floors to explore and special kids area where you pay for a session and go in with kid while they explore loads of hands on stuff. It took me ages to figure out how this worked lovely assistant at front desk where you get tickets for everything explained it all.
You have to pay to get in science floors upstairs but can just go to kids bit, small aquarium is free and has restruant in it, submarine (seperate ticket) and big silver ball to run around (think its a IMAX type thing but never had time).
My DD is 5 and loved visiting all the landmarks and seeing the Eiffel Tower twinkling at night.
Are you flying in to Beauvais? By the way Metro is great for getting around, if staying near Disney you will get RER train into Centre then you can get passes for 2/3/4 days that cover central Metro and I think buses.
We jumped on and off metro all day saves time and legs even though Paris is fairly compact you want to see the highlights and not lots of nondescript streets if you only have a couple of days.