Eli5 why grown ups do not fall down from the bed?

Question

I am wondering why small kids ( even a few years old) fall down from the bed while changing their position but bigger children /adults do not, no matter how much they move while sleeping?

In: 2276

Answer 1

I might roll to the left a bit, roll to the right a little bit, position shift, but I wont roll multiple times, so generally my starting position prevents me from falling off.