1. Eating habits
First-Schedule it. If breakfast is at 10, lunch at noon may be a bit early. Snacks should be scheduled and limited as well.
"Grazing" leads to kids feeling like they need to be shoveling something in all the time. Skinny children will go ahead and eat if they know when their meals are.
Multiple kids? You have probably noticed that scheduling is vital anyway.
2. Diet
Give kids a reasonable first serving. Personally, I do it all based on what I eat. My 9 year old daughters (twins), who are themselves different, get what I consider a decent first serving with seconds optional, seconds being for dinner only.
So-If I get 2 scoops of spaghetti, the twins each get a bit more than one scoop. My 6 and 5 year olds get a scoop, while my 4 year old gets less than that. Seconds are sized between how hungry they say they are, and past experience. I have been known to give a child a teaspoon more food and they were satisfied.
Also, reiterate the idea that you should stop eating when you are not hungry anymore. One of my boys is infamous for eating things he like until he is ill. I shrunk his portion while spreading it around so it looked like it was more, and established a time limit between finishing eating that first serving and getting a second. A cup of milk is filling as well.
Worried about cost of this? You'll have to overcome a few biases. Eating the same meal two nights in a row is fine. Every meal does not have to be three courses. Nutrition is important, but if the kids are healthy and growing like they should be, why worry about calories and such. If you're REALLY worried about nutrition, Milk at dinner, Juice at breakfast and a multivitamin will carry you through.
Oh! One of my money tricks is to serve the kids, and then see what the leftovers on their plates are. I'm their father and they have the same cooties as me, so I'll eat what's left. Scooping untouched, unmixed food back in with the other food works, as well, just watch out for kids to say "ewww!". This is a cultural thing, not a legitimate health concern.
3. Exercise
I set a minimum time limit outside, weather permitting. I take them on walks through our local state park. That's about it.
I don't force them to go on a daily walk with me, but I invite them. I don't force them to join little league or martial arts or dance... but I mention it to them, ask them if they want to try it or not, and if they do I seek out coaches/teachers and ask if they can try a session or practice with them. If they don't, I try not to worry about it.
The fact is, one of the best ways to create a sedentary child is to make physical play become a chore. Just chill out about it. Be encouraging without forcing it on them.
4. Common Sense
Look, if your child is twice the weight they should be for their height and eat twinkies for every meal, you have problems. The kid didn't start that way, you allowed it, and now you may have to fix it. Go to the doctor, get a diet and exercise plan, and learn to say no to your kids.
Your child's health outweighs all. Go see your pediatrician. Find one who is all about treating kids' illness, not pushing an agenda. Their advice should outweigh everybody's.
I hope this helps!
