Yes, sadly I think you will find almost all schools and daycare centers/preschools (home daycares will be different) require a store bought item for safety reasons (ingredients are listed on the label, and the assumption is that they were made in a safe kitchen that has been inspected for food service, etc..and then the ingredients and such can be tracked should someone be ill with some food bourne illness outbreak).
I know when I was a nanny in the early 90's, the kids I watched also attended a Montessori preschool a few hours a week..and that was when I first remember such rules coming into play. I had a conversation with one of the Moms, who would bring in these wonderfully elaborate cupcakes for some of the bigger holidays. She said she was able to do this because she had a caterer's license. It was as close to "homemade" as we were able to get when those rules were changing for them (with my oldest charge, we could bring stuff we made for parties, but a few years later with the youngest is when the rules changed around here).
I agree to get Silly Bands, or fun Dollar Store items, or some fruit chews or?? See what your class rules are on sweets and treats and try to be a little creative if you can?? I bet they get alot of pencils! LOL