Can low blood sugar cause bad behaviour in children?

No. Low blood surgar is dangerous as the brain and then other parts of the body are no longer able to function. Patients may become somewhat irritable and jittery and what they say often fails to make sense. They will often pass out and only if given glucose or glucagon will they survive. This is very dangerous. Make sure the intake of carbohydrate is adequate. Diabetics getting too much insulin same.
Yes. Low sugars can cause bad behavior in adults too. More worrisome is that low sugar can also cause poor attention in school/work and worse, seizures. However, unless one is taking a diabetes medication, the body will protect itself from excessively low sugars even after skipping a few meals (although one can certainly feel grumpy after just 1 missed meal).