I have seen a theory in other places that William was noticed during visitation with his bio mum/dad in a shopping centre. This theory seemed to develop after this piece of MSM info ......
Natalie said that after William was finally removed from Brendan and Karlie’s care, the pair had infrequent visiting rights and could only see him at a public shopping centre near Ryde.
Stunning new revelations about the day William Tyrrell vanished
This theory then goes on to hypothesise that William was tracked and then watched, and then was abducted while alone for a few moments in Kendall. That someone became obssessed with him, and considered his vulnerability as a foster child.
Personally, I lean toward the KISS principle. But everyone has their own theories. I don't believe that anyone actually knows for sure, except for the person who carried out the abduction, and the police.
This could be what our poster was alluding to?