Babies are born with the sucking reflex, so they suck on almost anything that touches their mouths — including their fingers.
Soon after birth, many children start to suck on their fingers or hands to self-soothe, relax, or explore their body. It is very common, natural, and as long as their hands are clean, a good thing.
How to support this development
Don’t discourage finger sucking. Allowing Your Child to learn how to self-soothe will give your little one an added sense of security, and will help them with regulating their emotions later in life. You can observe to find out what the little one wants and respond right away to help reduce finger sucking.
If you are concerned that the little one will not stop, you can get Your Child a pacifier instead.
Note: All children develop differently and at their own pace. For children born preterm, the referred timeframe for achieving the various developmental milestones might be incorrect.
Source: The information and graphs about when children reach specific milestones are taken from various sources, including the United States Center for Disease Control (CDC), the Denver Developmental Screening Test, and the State Institute of Early Childhood Research, Germany (IFP).
Ketsupa Jirakarn (Mental health specialist) (28 May 2021)