I used to advise on head lice as part of health product talks, mainly involving tea tree. For a start you will never see the end of head lice in schools while just 1 person has them.
Lice transfer when hair and heads touch. Short hair, the shorter the better, helps enormously in preventing it.
Use tea tree in a normal shampoo, and some in plenty of conditioner. Not added to the bottle but to the shampoo in your hand. Although it is generally considered safe, do not overdo the tea tree oil on children.
Every day mix a drop of tea tree oil with a little conditioner, or cream, or oil, that will wash out. Rub a little around the hair line, from above one ear, around the nape of the neck to the other ear. This is the area they usually settle on.
I had 2 cropped haired boys who fortunately didn't get head lice. I know many people who found the following useful. Mix ample oil, body or almond, with a few drops of t tree oil. Apply all over scalp, parting hair as you go. Cover with a shower cap. Leave for hours if you want. Shampoo out. Not sure if the t tree works or it is suffocation.