DS1 is ANA to egg and highly allergic to dairy (although getting a bit better with dairy). I don't like him eating any food made by other parents due to risk of error or cross contamination.
This is the opinion at our school as well. Could you take something that wasnt homemade? Ice blocks or those Oreo sticks in the blue packet are egg and nut free. Though I would take them in the day before so the parents could check the ingredients thoroughly before giving permission for their allergy kids to eat them.
Ice blocks like zooper doopers are usually more popular with little kids especially this time of year anyway and way less hassle for the teachers