you can always go to restaurants in hotels...

I didn't do this but someone in my family tried this. they're booked in santa fe but they had lunch in New Port Bay.
the best, in my oppinion is the restaurant in 'the' disney hotel.
in the parc itself:
Plaza gardens restaurant is one of my favorites,
It's a buffet so there is something for everybody and it's really comfy there

I think as a 5 year old son, he'll enjoy the Buffalo Bill wild west show.

it's not really a fancy restaurant but it's some entertaiment for kids.
If you don't know, there's always a restaurants and bar segment on teh site, maybe you can check that out as well

you can enter your budget, location,... :-)
http://entertainment.disneylandparis.co ... dex.xhtml#