I absolutely hate not having peanut butter as an ingredient for my kids' lunches and snacks because the school forbids anything with peanuts in foods they bring to school. I understand the struggle of having a kid with special needs in schools--one of mine has autism and the other an as yet incompletely diagnosed neurological condition (could be epilepsy, could be mundane ADHD, could be both--we're still testing). The school must accommodate these conditions, but that accommodation doesn't require banning things or reorganizing every activity around their needs.

Your kid will be just fine if some other kid eats something with sesame in it, unless they're sharing, kissing, or fighting with their food.