I think the cost to the child in order for the parents to learn how to parent Toby, in this case, would simply be too high.
Tiffany has problems from childhood, as far as we could see she had no family or close friends giving support. She isn't strong (who would be in that situation?) She is very vulnerable and quite likely to fall for another 'Mike'-putting her DCs back at risk. What she needs a a 'mum' living with them-a sort of kindly granny-to give her love and confidence and help her with the practical. Even if there was the money, it needs a real 'Mary Poppins' type figure to do it. (Judging by the hoards of people on here who have trouble with the family granny)
It is very sad but I don't think that you can risk the DCs ,while she gets her act together. They will at least be able to see the film when they are adults and understand that they were loved. Loved enough to do a really unselfish act.