Our kids pretty much eat what we do. We have three of them, 10, 9 and 4. Up to about the age of 5, we let them eat pretty much what they wanted to eat - at the preschool age, they need to have adequate levels of fat in their diet for proper growth, plus they need a balanced diet. We weren't too crazy about limiting certain items, except that they are never allowed soda or anything with aspartame (they do get the occasional soda at Grandmom's!).
As they get older, we really cut down on the sweets and "junk" that they can eat. We also require a protein source at every meal. They all eat protein bars (either Tri-O-Plex or Luna bars) as snacks and sometimes as breakfast. It's better than a pop-tart! We do allow desserts on a regular basis, but just a taste. I'm of the school of thought that moderate consumption is better than overdoing it because they've been denied.
None of the kids is overweight, and all of them have some knowledge of proper eating and bodybuilding. They see both Mom and Dad down in the gym, and they think that people that DON'T do that are weird!
I'll leave the second part of your question to CC to answer . . .