Elves!
The elf was dressed like an… elf. Timmy thought that was funny, because the elf didn’t look happy to be dressed like one of Santa’s helpers. The hat and pointed shoes looked real dumb on it, the green tunic was ripped in a couple of places to make it fit, and the stockings were all baggy. Timmy knew why nobody else was seeing this — elves were good at making your eyes lie to you — but it was still weird to see the elf just stand there.
Young and Thin hadn’t gotten Timmy’s made-up mother on the walkie-talkie, obviously, and they were trying to figure out what to do next. So Timmy had helped them out by saying My mom would be waiting for me by Santa! She’ll be there! The adults were happy to grasp at that straw. Once he got there, all Timmy had to do was shout Mommy, mommy! There you are! before ducking into the crowd. Young and Thin tried to catch up, but Timmy was able to get out of his sight… and then, just like that, Timmy had a different colored coat on and no brightly-colored hat and he was wearing a pair of thick glasses. Young and Thin went right past him without figuring it out.
The other adults didn’t see Timmy’s sudden switcheroo, either. They never did. He’d seen that adults hardly ever saw anything. It was weird.