a vinegar and water solution with a few drops of tea tree oil, in a spray bottle, spray on before school,to get rid of crawlies, smother hair in conditioner and comb through, with nit comb, do eery day or night etc, for a week, then 3 times a week for the next few weeks...till the cycle is done.

One of the girls I used to work with, had the same prob with one of her daughters who kept getting them, what I mentioned above is what she did, also keeping the childs hair up, in a tight bun (harder for them to get in) and liberally spraying with hairspray (i know its not really natural, but it worked for her)