Not sure about Australia, but in the US that isn't how it works. If Peter were to refuse to cooperate, there is no way CPS would let the child return while Peter were still in the house. You are right, call the lawyer NOW, while Peter is packing a small just in case bag, and have her meet them at the precinct with the arbiter from that mornings hearing in tow.
Unfortunately Droughtquake is right. I've seen abuse allegations through my work at the daycare only too often. Everything from an abusive father who fractured his daughter's collar bone try to remove her from the daycare in violation of a TRO to a false accusation from a mom who got caught cheating saying he was abusive to the children and she was afraid for her life, getting his firearms and all associated licences and ID's taken away. His "abuse" of the children? She claimed unnecessary medical procedures. The procedures in question? A mouth swab for DNA testing to see if the two toddlers were actually his, since he found out the cheating dated back to before their wedding! (I would have had them DNA tested too!)
My point is, the authorities have to investigate EVERY case as though a child's life depends on it. The sad truth is that it very well might!