My stepson gets lice everytime he comes to us from his moms house?

This has been happening for over a year. He lives with us half time and everytime he comes back from being with her he has lice. He's only 4 years old! We have used the shampoo so much his hair feels so brittle now! We don't know what to do anymore. I've gone thislong w/o getting it. But I would feel horrible if my 7month old were to get bitten by one! Can we call cps or something like that so she knows we're serious?? Any advice is appreciated. Tia.