It is entirely possible that starting the day without a decent breakfast could snowball. I have low blood sugar. If I don't eat when I get up, I get a stomach ache, I get grumpy, sometimes it'll even make me feel sick if I don't stop and make time to eat. At the point when I start to feel sick, I don't want to eat anymore.... and I graze just as you pointed out. I would mention it to the parents for sure.