Maybe you should go to the school admin, do a small presentation for them. After seeing it , maybe they would be better able to support you to the parents, or maybe you could do a presentation to the parents as well. Be flexible, but approach it in a dignified and intelligent way. If they can see the snakes before hand and you can "prove" to them that their is no undue risk presented to the children, maybe they would allow you to still do you presentation to the younger classes. Just a thought. It sucks though. That's why we are teaching our child about all kinds of animals and their care, so that if somone want to bring a 4 ft yellow anaconda to school to educate, then that is fine with me. In fact I would probably be there just so I could look and appreciate the beauty of it.