The area is tree filled. You could probably be out of sight in 10 seconds from a person at a fixed point like a window or a seat on a balcony.
I don't know why people are so resistant to the idea that someone could have taken him unseen and unheard. I understand that kind of necessitates an abductor who was laying in wait, maybe just to grab a glimpse, maybe with the plan to take the child(ren) if they could. But as far as logistics go, I don't think it was particularly difficult for someone to be out of sight in the timeframe suggested. People can steal your wallet bumping into you on the train without you realising. They can certainly be out of your sight in seconds in a house surrounded by trees especially if you don't know you should be looking.
Firstly, the "someone" was a 3 year old child. A 3 year old who was in unfamiliar surroundings, being watched over by a mother and grandmother, wearing a highly conspicuous outfit, full of 3 year old energy and jest. Children of that age don't have the capacity to sit still, or to be quiet for any lengthy period of time, unless they are asleep, and they don't have a developed attention span, in fact they don't have very much developed at all, in comparison to adults. Given William was in unfamiliar territory, surrounded by bush, is even more reason that his caregivers in all probability would have been watching him more carefully to ensure he didn't wander off, get bitten by a snake, or whatever.
Secondly, given the nature of the location, with houses in sight, it would be highly unlikely no-one at all would have witnessed or heard something unusual such as a car. In fact, most especially being such a quiet neighbourhood - people notice when something is "different" in their street. Further, neighbours who are not used to having small children in their street, tend to take more notice when they are there (because it is different or unusual).
Thirdly, someone stealing your wallet by bumping into you on a train not even remotely similar to this scenario.
My point is, both plausible scenarios are becoming more and more implausible. I am only able to think of two cases where a child in that age group has been abducted during broad daylight hours from their residence who wasn't personally involved in some way with the child. One instance was from an apartment block, and the other from the front yard of a house - both from neighbours, who were drug users and had mental problems, in very different demographics. It didn't take the police long to ascertain who the culprits were. Children of that age group are usually abducted from their place of abode during the early hours of the morning, when everyone is asleep, as there is less chance of being caught. The police themselves are at a total loss to explain how no-one could have seen or heard anything, just as they are at a lost that they has been no evidence gleaned from the search, in either the abduction scenario, or the wandering off scenario. As a few people have pointed out, it would be very unusual for no evidence whatsoever to be found, such as fragments of material from his spiderman suit, or a lack of scent being picked up.
I think some people are only resistant to the idea because it is so unlikely - not that it couldn't have happened. Obviously something untoward happened to William, as we only have the 2 scenarios to work with, it could be either.
