From the Missing Kids website: 86% of child trafficking victims were in the care of social services when they went missing. http://www.missingkids.com/KeyFacts

That's for the US, though. I'm not sure how Australia fares in that area, although I'm sure it can't be much better.

Yep. This happens a LOT.

"Recent sting operations revealed that more than half of the children being traded for sex come from foster care. The same children identified by our courts as most in need of protection from abuse and neglect are being bought and sold everywhere from truck stops and cheap motels to wealthy suburbs. They are being used, reused, and then discarded like trash.

What makes it all the more appalling is that, in the vast majority of cases, no one even looks for these children when they go missing from the system.

‘Research shows that most victims of child sex trafficking come straight from the foster care system. This is totally unacceptable,’ said Rep. Dave Reichert, R-Wash."

http://medicalkidnap.com/2016/04/15/the-u-s-foster-care-system-modern-day-slavery-and-child-trafficking/

the grandmother had connections to two known paedophiles named as persons of interest in the case and she ended up with a warrant for not turning up in court in relation to the matter

http://www.dailymail.co.uk/news/article-3754492/Best-friend-missing-toddler-William-Tyrrell-s-grandmother-questioned-police-disappearance-pair-mysteriously-try-buy-home-together.html