This situation is difficult. Who knows the full facts? They cannot be published because of the right to privacy.
No social worker can take a child away from the family home without a court order. So it's not social workers who are 'to blame' here, if anyone is to blame.
Foster care is not a panacea - it may have downsides and long-term after-effects. A court will have to balance these against the risk the children are facing now.
Clearly, any mother who prefers to live with a convicted paedophile needs her head testing - but this does not necessarily mean she should be prevented, legally, from doing so. There are many wicked, unthinking and crazy behaviours that are not necessarily illegal.
I can imagine that there have been many strands to this story. We can't know them. What if the paedophile in question only goes for young boys and claims girls have no attraction to him? What if he claims to be a born-again Christian? What if he says he is truly sorry and he will never do anything bad again? What if the mother believes him? On the face of it, all these claims are weak - but the court has to examine them and decide.
Locking girls in their bedroom to protect them is horrendous - but we cannot know if this is the least awful of all the alternatives, because we don't know the full story, or even if what has been reported is true.
It's no good saying 'why can't relatives take these children?' because not everyone is capable of or willing to do this, and it cannot be enforced.
Whatever the situation, it's an awful one, but no one can assume we have all the facts here, and not sufficient to have an opinion on the court decision.