T.M.
Just buy the Nit-Free Terminator Lice comb from Amazon. It’s about $10. Run the comb through your son’s hair every day to every other day starting at the roots and working down the length of the hair. This will prevent any nits from sticking. I’ve used Fairy Tales before, but frankly only after we’ve had an issue. SO, not sure how well it works to prevent it in the first place.