First thoroughly wash the kids hair with lice shampoo and a nit comb. Shampoo and disinfect your entire house and discard thoroughly and items you supect may have become infected.
The best option for you will be to shave your child's hair to about an half inch length. This is because long hair often does not get combed thoroughly, and if you do not comb it enough, the lice eggs will hatch once again.