I have not noticed the same things about the kid's menus that others have said. We don't eat at many CS places- so maybe that's the difference?
Most TS places will have different menus for kids- it's not the same menu park wide. My kids do not like fried foods, and have never had trouble finding alternatives off the kid's menu- pastas, grilled chicken, rice and veggies, apples and grapes, applesauce, fish choices, etc. Most restaurants around the World Showcase will have menus that reflect choices from that country.
This is also true for Yak and Yeti. They have a great kid's menu!
As for buffets- no one cares what you choose to eat at a buffet. Kids have an area for themselves- but adults can choose from that section as well as children eating off the other sections of the buffet. It's not something that is kept separate or is monitored.
Buffet food is for everyone to help themselves.
-Sarah