Don’t turn on the light
Nowadays, kids sleep with some light nearby, like one in the hallway or in the bathroom, but during Victorian times parents were told leaving the lights on could mess with the kid’s nervous system.
Babies have to sleep on their stomach
In the 1980s the norm was that newborns had to sleep on their stomachs because sleeping on their back was seen as a choking hazard. Since the 90s, though, pediatricians recommend that newborns always sleep on their backs.