I mentioned that I'd had good luck with getting my roommate's son to do jumping jacks and "run his wiggles out" when situations with too much energy + too much sitting still arose. Maybe the hint will help her later on.
She was entirely occupied with the baby, and getting the stroller folded for the bus. It finally took help from one of the random youths around the bus stop to get the thing folded. She was tired and cranky, and the kid was obviously not tired enough. He was wiggly on the bus, and wanting to do things like pull the cord. (He was, to his credit, waiting until after someone else had actually pulled the cord for the stop before pulling it himself, reasoning that someone else was already getting off. I can sometimes follow four-year-old logic without having it explained.)
In the seating scramble, he had wound up in the back corner, and I had wound up in the middle of the back seat. So I was sitting generally next to him, with some space in between.
I'm always confused about what to do when there's a situation with a bored kid who I could probably help entertain, but the kid is a stranger. I do not want to be overly familiar and therefore spooky. I do not want to invite the child to violate their stranger-caution training.
The kid wound up clapping, and I clapped back. This turned into a clapping game, after the kid went through the process of "I clapped. She clapped. I'll clap again. Woah! She clapped too! I'll clap. Yes! She clapped! I'll clap. HEY! SHE'S PLAYING WITH ME! NOW I CAN HAVE FUN!" The clapping game turned into a game of mirror, where he'd touch a body part, I'd touch mine, and eventually involved things like claws and making faces. Things were getting very silly by the time my stop came up, and I asked him (the first time I'd spoken to him) if he could please pull that for me, because this was my stop.
His mom was happy that he'd been occupied and not causing trouble. Yay!