The whole idea of fasting especially at this time of year, is ridiculous nonsense.
I believe that Muslims do not insist on their children fasting. However, the school must cater for those that might. At this time of year a child would be required to fast from just after 4:30am. This would mean them having breakfast at about 4am (and thus disturbing their sleep). By the time school ended they would have had no food (or, more importantly, drink) for around twelve hours. This is a dangerous state of affairs, especially in high summer, and the school is right to be concerned.
Yesterday there were reports that a school had confiscated Scotch Eggs from pupils' lunchboxes because they were deemed "unhealthy". This is beyond the school's remit, in my view. But this school is perfectly justified in these concerns. If Muslim adults are daft enough to follow this ridiculous practice that is for them to decide. They should not expect to inflict such stupidity on their children and if they attempt to do so then schools that have to ensure their wellbeing during the day should simply refuse to have them in their care.