I agree totally too. But I still think it's even more of a 'freak' case than, say, abducting a child walking to or from school, or from the side of a road. In the former scenario, the walk may be part of a child's routine. In the latter, it may not have been part of a routine, but the window of opportunity may be a lot larger (thinking of Daniel Morcombe) than with William.
If it was an abductor, he wasn't hanging out near a school or playground. It wasn't during school holidays. Although perhaps the person was targeting pre-school age children in particular. An abductor, if a stranger, could not have known William would be there as it wasn't William's home. However, perhaps such a person had a plan as to which area he planned to abduct a child from - somewhere around Benaroon Drive. And William just happened to be there. Alternatively, a person could have spotted the family the day before or on the way up from Sydney, and followed.
I know we aren't meant to keep discussing foster/bio issues as no facts have been stated. What has been stated as fact by police, and reported in msm, is that police were working together with DOCS on this case. That, to my knowledge, is not routine for all missing persons under the age of eighteen. So whilst we don't know precisely why DOCS were brought in, we can assume that there is a 'child protection' matter of some sort in relation to William.