You asked a WWJD question......that is all-encompassing question: What WOULD Jesus do? The right thing....Uphold Christian values....whether it be helping a mom find a job other than taking her clothes off for money, helping someone get off drugs, or abortion.
Jesus would also recognize that the mother is in charge of the child....and he watches us do stupid things every single day. It's that free will thing, again.
Bottom line, put the kid in public school if you don't want an agreement that the school will teach your kids Christian values.
I think Jesus would say keep the child in school, and pray and work with the mother.