1 acre for under $200,000 in a rural location, close to town, really nice homes, is cheap & I wouldn't be surprised if it's attracted a lot of enquiries. AND A LOT OF LOOKERS. So it could be anyone!
Mind you, anyone who had previously gone to look at that block of land would most likely not have been there at a time that William was in the house opposite. There is of course the chance that someone happened to just be there on that Friday morning and picked up William on the back of looking at the land...
I just did a Google Earth scan of Benaroon Drive, to try to get a better feel for what kind of visibility of the environment there is from each of those houses. It is true that the overall visibility down the street from William's grandmother's place is fairly unimpeded and that a foreign car lingering around the place may have stood out.
For this reason, I am more inclined to think that William might have been watched from an adjoining property. I don't even picture how he could have been lured into a car. I realise someone could have promised to show him something, but at the same time they would have had to hold his mouth shut most likely to stop him screaming, they would have had to open and close at least two car doors - somehow just too much 'commotion' and hassle. Plus, any minute the sister or mother could have come back out of the house.
I am more inclined to think that someone from somewhere could have called him over and lured him into a house or into the confines of another property. I just feel that a small child, in that geographical location, could disappear from view more swiftly that way, than by means of bundling him into a car.
It would also leave the person with an 'out': should he or she be seen, they could always come out with something like they wanted to show William something at their place. That would be more plausible than someone being caught bundling William into a car having to come up with a reason for doing that!