The exact same was said about CS's abduction. No one would go to a an isolated spot with children at 6.30 at night. The majority of the public did not believe anyone could enter a tent with parents asleep inside and sneak out a child.
The parents were abused, threatened and villified by the public for their interviews and how they responded, how they drove around looking for their child and didn't wait at the tent, why they even went camping with kids in the first place, the way she was dressed, her parenting style, one parent being a step parent so........
Yet while many members of the public immediately suspected the parents, the police soon established there was an outsider in the camp. If the CS scenario had happened in William's case, a neighbour would have stepped up to confidentially tell police he/ she had had a visit from a contact selling drugs. These neighbours were in their usual quiet street, so they were more likely to identify someone out of place, and could have told the police. Tradesmen, verified visitors etc could have been ruled out, but there could have been another "doll collector" in the bunch.
Yes, it's possible that a child could be snatched off a culdesac but it's extremely unusual that nobody saw or heard anything when even an unverified car would stand out.