Maybe you could get a separate insurance policy. I have up to $2,000,000 through Secura for selling honey if anybody gets sick/stung/chokes on glass ect...for $284/yr. I'm also LLC so don't know if that affected the rate or not, but might be worth looking into, being that it's a school I'm guessing you'll be out of luck. Even if you get insurance I'm sure some parent will freak out and cause a ruckus.