Head lice can be an embarrassing subject, but small children can come home from school almost on a weekly basis with them, and the over the counter remedies are expensive and dangerous.
On dry hair, saturate the head with simple baby oil, this will immediately suffocate the living headlice. Put a towel around the child's shoulders to prevent ruining their clothes and leave the oil on for ten minutes
Then using a PLASTIC nit comb, comb through the child's hair until you can't find any more lice (a good rule of thumb is to comb ten times without finding lice, then you know you've got them all)
Then, section off the hair and while combing with the nit comb, put a hair dryer on as warm a heat as the child can stand (not too hot, otherwise the baby oil will fry their head!) and this will remove the eggs from the hair shaft
Pat the excess oil out of the hair with the towel. Then, without using water, soak the child's hair in shampoo (if you don't add water then it emulsifies the oil much better) then wash it out. Wash the hair as normal, and voila! Headlice are gone!