Should I try to stop my baby from sucking her thumb?

No, you don’t have to stop your child from sucking her thumb while she’s a baby. Babies generally suck their thumb to soothe themselves, which is good, because they need to learn how to rely on their own resources.

The ability to regulate or control one’s behavior and emotions is an important developmental challenge. When your child sucks her thumb, she’s finding ways to make herself feel better without your help.

In general, thumb-sucking is more irritating to parents than it is harmful to kids. Your baby will stop when she’s ready and has developed other ways of soothing herself.

https://www.babycenter.com/baby/baby-development/should-i-try-to-stop-my-baby-from-sucking-her-thumb_6817