Parents feed your kids before class. It helps us as coaches to keep the class running smoothly and without distractions.
Maybe I am taking this the wrong way but it sounds kind of snippy to me. Do you have any children of your own or are just a coach? By your reply, I think not. And, if you teach this age group and don't give them anything, then you may want to re-evaluate because I am willing to bet you have a group of nasty, grouchy, un-productive girls on your hands! My daughter is just 6 and I am sorry, 4 hours is just too long to go without a snack break. She is very physical already and not a big eatter throughout the day, to stuff a couple crackers or a cereal bar in her mouth in between the different stations is enough to keep her going.
I am not saying you need scheduled snack time, but when you send them for water (you do allow them water don't you?) allow them a quick fix.