If you activate testing cheats on and shift, click on an infant, the option to age them down is there. And when I tried it on, I thought he’ll turn back into a cute baby. But well, this happened instead. Not sure which is worse, the fact that he turned into this horrifying headless spider like demon from the depths of hell or that he wore an outfit from the Star Wars game pack. For some reason in the game, his portrait has been updated into this innocent looking baby. The game also considered him as a baby. Yet this thing produced adult sounding voice and what seems to be adult idle animation from time to time. I also can do anything when playing as him. Don’t worry though, I solved the problem by moving the baby out of the household where it finally turned into a regular baby.