I'll accept that as a valid argument for being purely looking after the welfare of childeren if the school did same to Jewish or some other powerful lobby's kids as well i.e. denying them something that their religion or traditions expects from them.
If only Muslims are being singled out for one pretext or the other, it is Islamophobia.
PS. Islam does not ask kids to fast. If some parents want to force it on their kids, they should be taken to task. And no, i am no religious authority, just an average Joe.