When I have kids, I think I'm going to regulate fasting for them a little differently to how my parents did for me. Before I actually studied Orthodoxy, I had a very legalistic type conception of fasting. Fasting was not about sacrifice and self-control, it was simply about "you can eat this" and "you can't eat that", and I always managed to find ways of getting around certain foods via technicalities e.g. we had this fantastic "fasting cheese" that tasted better than the real deal, it was unbelievable! I would like my children to understand the essence of fasting through experience; i would like that very essence to be instilled in their minds, their conscious and their hearts from the earliest of their years, rather than it being something they read about later on and try to adapt to. As such, I think for their first fasting years at least, that I will be more concerned with teaching them to abstain from the foods they love the most, even if those foods do not technically qualify as non-fasting foods (such as candy for example). I would furthermore still allow them to eat of those non-fasting foods that they require for their concentration, focus, strength, and health (though upon certain conditions), until they're able to better appreciate the value of such food. For example, I may allow them to have meat for the sake of keeping up their protein levels, though I would teach them to abstain from the type of meat that they would really enjoy such as a McDonald's burger, or chicken nuggets. As another example, I may allow them to have milk for the sake of keeping up their calcium levels, though I would teach them to abstain from say chocolate milk, or chocolate in general.
This, ofcourse, is simply my personal opinion on the matter, and one that I would consult with a spiritual adviser first.