Rather than just improvising with such young children and risking harming their health, perhaps you should do some research and reading. There is a Sugar Busters for Kids book and I think there is also a Carbohydrates Addicts book aimed at parents of younger children. If I were going to put kids on a lowcarb diet, I would read these books.

I always debate how to answer questions by parents who want to put their kids on diets. My parents put me on many diets as I was growing up and the end results was that I developed eating disorders and became a fat adult. I strongly recommend against putting pre-adolescents and adolescents on diets. You write yourself that your 11-year-old is slimming down as he grows. Your 9-year-old may well do the same thing.

Both my kids put on weight in the pre-adolescent years and both slimmed down as they went through their growth spurt (my son is 6'2" and 150 pounds and my daughter is 5'6" and 120 pounds). My son stayed at 150 pounds from 5'6" to 6'2". I never discussed dieting with them, although I did discuss healthy eating. Neither has developed an eating disorder.

If kids ask their parents for help with losing weight, I think the parents should help. Based on my personal experience (both myself growing up and my kids), I think that parents should be very hesitant about imposing a diet on their kids. Adolescents love to rebel and putting them on a diet gives them a wonderful opportunity to do so.