The Problem with Chip's School

So, there was this not so little problem yesterday at Chip's school. He is two and goes to a daycare/preschool around the corner. Chip rarely eats breakfast in school, but yesterday he ate pancakes. Which would not be a problem , but he is allergic to eggs. And the school knows it.

When I went to pick him up at 4:30 in the afternoon, Chip's face was slightly swollen and he had hives. When I got home, I looked at the daily report (which said he ate pancakes) and called the school. The most disconcerting thing was that not only nobody noticed his hives, but nobody would own up to the mistake after I called.

I am reluctant to change schools because Chip likes his teachers and has adjusted to his new environment, but I am at a loss on how to deal with the situation. Do I write to the director? Have a meeting with the principal? Would any of this mean my son will be treated differently? Or should I just hope everybody has learnt something from this and cross my fingers and hope for the best?