My two favorite places in Waitsfield are The Green Cup
I am not sure how kid-friendly the former is, but it is definitely worth finding out. It has been written up by Mark Bittman of the New York Times, and I had one of my best Vermont meals there. The latter is a tea room and vegetarian restaurant owned by a couple who recently moved here from L.A. I really enjoyed the food and ambiance last time I was there, and felt very healthy and wholesome thereafter.
There are some good localvore places in neighboring Warren, too. Let me know if you would like to hear about some additional spots!