I highly recommend that you post these at every workstation so that the information is highly conspicuous. The Internet is full of places that are inappropriate for children. For children, this means that their parents must sign it as well. Beverage and Food Do not allow any food items in the classroom. This is for obvious reasons.
Nothing destroys computer hardware more quickly than the knock of a hand against an open beverage.
Food crumbs are also bad as they get caught in between the keys of the keyboard and in the moving parts of the mouse. This rule is more important than you might think. In fact, if you are required to troubleshoot your own computer problems, this rule is vital to your administration of the machines. Students will turn off the computer when they are done, requiring sometimes lengthy boot-ups before another student can use them. Make sure they understand to leave the machine on.