Annaliese, at 2.5, is doing arithmetic.
We have a program where, for peeing in the potty, she is rewarded with a gummy bear. For #2, she gets 2 gummy bears.
Yesterday she was explaining this to me, confirming the deal before she went to the bathroom, and a light went on. She said, "if I poop I get two gummy bears and if I pee I get one gummy bear. So if I poop and pee I get 3 gummy bears!"
That's not the deal, it's one or the other, but I was so tickled I agreed. :)