I've talked to CPS several times about untreated head lice. In the Lone Star state having head lice is not considered neglect (unless it has deteriorated to a scalp infection or something like that). But it is considered neglect if, because of the head lice, the kids can't come to school and have excessive absenteeism.
My district does not exclude kids from school for head lice.
But my experience with "these cases" is that the parent simply isn't interested and passionate about resolving the problem for...whatever reason; 6 kids, 1 kid, single, married, employed, unemployed, etc, etc, etc.
So unless your district excludes for head lice, you've done all you can do...forget about it.
Here's when I gave up on putting too much effort into something like this. Married mother of 4 kids, all of whom have head lice, family has medicaid coverage, parents won't take them to the doctor, I call the kid's pediatrician and beg them to write a prescription for head lice treatment for all the kids, pediatrician caves, emails a prescription to the pharmacy, notify the parent, and they never went and picked up the medicine - remember - medicaid, no cost to them, pharmacy located in the primary grocery store in town so I know they go there for food...what else can you do...forget about it!