Have them get a fine-tooth comb. Comb the hair from close to the scalp all the way through to the end 2-3 times (if the hair type allows it). Lice are tiny and therefore difficult to see, but the comb should pick up any eggs. The eggs are small, round and light colored. To get rid of lice requires a lice treatment (OTC) and laundering all bedding, clothes, hats, etc. In *hot* water. If anything is missed, the lice just comes back, or goes from one child to the next.
A simple way to check for lice is to hold your head over a light-colored towel and rub it slowly. You will figure out quite easily about the presence of mice.