Do you think Sophie keeps them away from school as she's scared they might tell friends and teachers exactly what is going on?
I think she keeps them out of school because she wants to keep them as illiterate and poorly educated as her so they don't start questioning her lifestyle. Dumb them down so that they have no option but to sell themselves too.
Imagine if they actually were at school, learning and passing exams, having their horizons broadened beyond tiktok, tacky outfits, old men, and plastic surgery, and being exposed to far more functional families via their friends? Better to keep them isolated. She is so low, I can't understand why she would want that future for her children, she is totally unfit to be a parent.