They didn't ask for a unemployed crack addict mother and an unemployed convict father, and yet the state seems to have given them back to both the unemployed crack addict mother and unemployed convict father. They were living in different, perhaps better, circumstance before they were returned to their biological parents. Why not leave them in those circumstances and instead allow visitation of the parents until they can quash their demons and secure a job instead of holding up the "family must be together" mantra and having them live in this hellhole?
Fosters home are often incredibly bad. I have been told by foster parents to keep your kids out of that system at all costs. (Those foster parents obviously cared about their children, but they've also seen children come through who were previously taken in by someone else just for the paycheck.)
What about things like freely available contraception and decent sex education at school age? I often read that there is occasionally opposition to both in the US.
China use forcible sterilization programs, which is one of those ugly and socially unacceptable answers, for good reason. (The US had a similar program. To give you some idea of how well it worked, the case that decided the constitutionality, Buck vs Bell, involved a woman who was considered mentally feeble due to being black, poor, and getting pregnant at 17. Turns out the last one was most likely due to her being raped by a member of her more respectable foster family, who committed her to an institution to cover it up. The whole thing was deeply fucked from the very outset.)
Forcible sterilization is not a substantial factor in enforcing the policy in China - it's enforced through fines and exclusion from all kinds of benefits.
Open that door and you get a whole world of ugly answers and precious few good and/or socially acceptable answers.