Hi Bethe,
My children are aged 11 and 13 and their favourite restaurant in the Magic Kingdom is Crystal Palace. This is a character buffet, the food is good and plentiful and you normally get to meet Winnie the Pooh, Tigger, Eeyore and Piglet. If you would prefer a non-character meal and like Italian food then Tony's Town Square is good, this has a Lady & the Tramp theme which is very cute.
At Epcot we have so many favourite restaurants, for characters it has to be the Garden Grill with Mickey, Pluto, Chip & Dale. We also love Coral Reef where you dine under the sea with turtles and fish swimming by and our absolute favourite is Teppan Edo in Japan. Here they cook the food directly in front of you which my children really enjoy.
There are many other restaurants in WDW and you can see some information on them all by clicking
HERE and then choosing either Magic Kingdom or Epcot. Once you've made your decision you can make a reservation by either calling 407-939-3463 or using the online system on the link above.
Hope that helps and you find a restaurant that all your family will enjoy,
Jo