my neice rocks back and forth in a chair/car seat often, why

I'm 50 and I've been rocking since able to sit up as a baby. It's never interfered with anything, except I sometimes still get a few strange looks. I've got several colleagues who do this too, it's more common than you think.

Don't let it worry you. I'm still rocking at 50. I'm PhD educated and have a wide range of interests and friends and a good sense of humour, maybe a bit nerdy. People are always going to judge you for anything, I say if they're talking about you, they're leaving someone else alone