In this case I'm assuming it's not a blanket rule. The OP states clearly the reason is due to children who have allergies. Food is very hard to contain, depending on age. With small children and hygiene (as you'll know with colds etc and how quickly they pass on) it's problematic. And I seriously doubt anyone would have the time to clean every surface after feeding times, including floors and chairs. Which is often why kinder's have stricter rules than primary school (aside from nut allergies all other allergies are specific to the classroom) and in most cases in high school it's up to the individual to keep safe.