I doubt its a cult child, Cults aren't common in Australia.
We just aren't that religious.
The clothing too - very main stream. In fact I had to double take, so similar was it to my own daughters clothing. She's a regular Aussie kid.
As far as incest goes - most children of incest are born just fine. Its when you have a genetic weakness that the risk skyrockets, but even then its no guarantee you will have a damaged baby.
They haven't been able to get DNA yet but when they do - my bet is there will be a familial ping somewhere in the criminal database. (HOPE)
If the baby is from Murray Bridge, the chances that its parents are in the system are huge.