[vosper]

Sleeping on the back only matters when they are very young. It’s for when they don’t have the strength to turn themselves out of a face-down / suffocating position. That’s why you practice tummy time (neck/head lifting) with an infant. Once they are older they can sleep how they like

[Enginerrrd]

Depends on the kid too. All 3 of my kids could lift their head up when they were born. A couple of times I forgot all babies aren't like that and picked up a friend's baby without adequate support.