Having another options of foods for kids who have allergic problem or special health condition is way different than allowing any religion to interfere in something (school) which is supposed to be without any religious influence at all.
First, it's like saying "Those kids are differents" in a place where everyone is supposed to be equal.
And second, it's the open door to any possible request about anything because "It's my religion."
presumably you also have an issue with schools offering vegetarian meals? since its basically the same thing