fyi, i'd be doing daily checks of not only your kids, but you and your husband and anyone else who lives with you as well. if the kids do develop lice that they got from school, there's a great chance that it may already have spread through your home as well. my girlfriend knows of this all too well. their whole family had to be treated. and because their school (which is private) doesn't have stringent lice policies and they allow the children to return as well, her children (and many others in the school) were re-infested multiple times after being given a clean bill of health by their pediatricians and school nurses.
i know that it's just hair and that short/no hair isn't usually as stimatizing for males as it is for females, but personally, i think shaving a child's head is extreme (an infestation that can't be under control is another issue). it's not as difficult as many people think it is to rid natural hair of lice and their nits. the major problem (from what i've witnessed) is when a "clean" child is returned to a lice-ridden environment.
good luck. i hope the exposure at your child's school is mild and passes quickly compared to what people i know have experienced.