Hi George, There are several things I would do in response to this situation.
>Contact the school principal.
Ask about the school's policy with regard to live animals, particularly snakes, being brought on campus by members of the school community. Share about your mother's experience, and ask for the principal's help in ending the taunting. I'm including a link below to Education.com's special edition on bullying, as you may find some helpful approaches within it for addressing the intimidation occurring with the snakes at school.
>If necessary, contact the school district.
If you feel your concerns aren't being addressed adequately at the school level after you've talked with the principal and given him/her an opportunity to respond, then contact the district about your concerns.
If you don't have the contact info handy for the school and/or the school district (and if it's located in the United States), you can research that information in SchoolFinder:
http://www.education.com/schoolfinder/
Some districts have an Office of Environmental Health and Safety (such as the Los Angeles Unified School District:
http://www.lausd-oehs.org/missionstatement.asp), which issues policies related to live animals on campus. Here is a sample bulletin from LAUSD's OEHS:
http://lausd-oehs.org/docs/Bulletins/BUL-3845.pdf
Find out if your school's district also has an office or governing board like this, and what their policy is with regard to live snakes on campus.
>Try to learn more about the snake being brought on campus.
Is it dangerous or harmless? According to the Humane Society of the United States, the vast majority of snakes who share human habitats are harmless, but all snakes can bite if threatened or handled.
http://www.hsus.org/wildlife/a_closer_look_at_wildlife/snakes/
Is the snake being used for a classroom lesson, or just being carried around by its owner (like a dog)? Is it loose (around the owner's neck or arm), or on a leash? It would help to have as much information as possible when approaching the school about the issue. Having factual information about the snake and/or risk of danger may also help with addressing the fears your mother and the children are having with regard to the snakes.
I wish you well as you address this issue -- at the very least, I hope your efforts help bring the taunting quickly to a halt.