in the hospital where i work, the policy is to stop eating and drinking from midnight. both for adults and children.
(the surgeons always make their program starting with the youngest,which can be of help according compliance to the fasting)
the only exception that we make, is to let babies drink milk up to 6 hours and sugarwater up to 2 hours before surgery.
in my opinion, when you explain the reason of the fasting to children (from 7-8 years, depending on the child) they really do understand and are proud if they can do everything you ask them on the day of surgery.
if the parents cooperate aswell, i think there is very much you can ask from a child, it is definitely worth the time you spend talking to them!!
hope this helps