Only speculation here:
I still think Kyron visited the electricity project with his stepmom and then they continued visiting the other exhibits in order to cover it all. I feel Kyron didn't get enough time at that exhhibit and couldn't wait to run back and take a second look at that project. He may have even lagged behind his small group later (if he was with the small group in fact) to look at it once more. His seeming fascination with that might have left him open to being offered the chance to see something else electrical in the building by ANYone --- a father, a science guy, a visiting worker from electric, cable, whatever company... I also want to know (if this was an impulsive act on a perp's part), was there any advanced project in the school that involved chloroform? To quickly silence a child...
Also think if Kyron was seen by a door, that he might have been waiting for someone who arranged to either pick him up after he took another look at that project, or someone who was at the school and had told Kyron that they'd get their car and swing around to the south exit and for Kyron to watch for them and then come on out to them. (I'd guess it'd be very busy with visitors leaving around 8:45 because the students then had to group in their classroom.)
Also thinking about large coolers, or (someone else's idea) a case for a large musical instrument, a large tool box, or any container with material for the talent show. I have a feeling that that might be the kind of thing the island is being searched for... a container or case?
Unless a perp felt VERY comfortable with the school, the rooms that locked, etc, wouldn't he get Kyron away as soon as possible so no-one would stumble upon them?