I can't speak for Williams NSW foster care situation, I can speak of my brothers however..
By the time my brother had his first child with his current/ex/don't care to know partner she already had three kids in the system, at that point she had had many chances to improve her parenting yet didn't... (Not that I'm laying blame on her or my brother... addiction does destroy us in so many aspects) she had tried and failed getting them back and these 3 kids were in the process of permanent adoption she still had one child in her care... She then had my brothers first two children and when the youngest was a month old, then those kids were taken and put in foster and a year later (my brother relinquished his rights as he realised he wouldn't get them back) and they too went up for adoption, in the last month or two they have now taken another child from him and this woman who was nine months old...
They give lots of chances and sometimes there can be kids already in care and kids still at home.. Twisted little system and I unfortunately am scratching at the surface, after two years in still fighting for access to those kids (because they were already adopted and we weren't informed I am unable to seek custody of them)
Hope that explains a little bit more for you what can happen within that system