On our next trip DS will be 10. He is a very picky eater and really doesn't even eat that much. At table service restaraunts, will he be able to order off the kids menu?
Although things could change at any time, my DD (16) still orders from the kids menu on occasion with no problems. You should be fine. I have heard that sometimes you are charged a higher price and given a larger portion but that hasn't happened to us.
A couple of years ago, we went to Whispering Canyon Cafe, and my wife (30's) didn't want any of the regular offerings, so they let her get a PBJ off the kids menu. Regular price, even.
I think this is pretty much the norm, but there might be places that wouldn't let you.