Ditto for what Rachele said.
We provided all food, including meals and snacks being in preschool and
currently in elementary school. It is not only safer but it will give
you peace of mind knowing that YOU have provided something safe. The
only problems I have ever had with reactions in school was a milk spill
and one time when a teacher said "I thought this was okay" . . . but she
didn't call and ask to double check.
Trust us on this one. We've been there.
Deborah