I think the doctor's appointment was for the school, not Kyron. I think she lured him out by saying he was going to get a special treat for doing so well and he'd be out of school for the rest of the day. She probably said, if he asked, that they would come back and get his stuff and the diorama the next day. I do think she might have said she was going to take him to see something cool that was electrical. I think he was told to meet Aunt Dede at the South door while she went out another way. If there were two white trucks, Dede puts him in a rented white truck while Terri drives off with baby K in Kaine's truck. I don't know who does the deed, but I'm guessing it was done by giving him sort of treat laced with an odorless, tasteless poison so there wouldn't be a mess. I really am thinking there might have been two white trucks, which is why Terri didn't care about Kaine's truck. Maybe the crime happened in the other white truck? Maybe they're trying to track down this other truck, hoping there's a crime scene in it? It doesn't matter how well it's cleaned out, forensic evidence could still be there.
Anyway, man, I saw the pics of the steps and immediately could see him walking down, using one of the rails for help. Oh Kyron, what happened to you? What lies did they tell you? You need to be found...