My 4 month old son always suck his hands fingers ,even after feeding him. I m afraid of that later on he will suck his thumb? I dont know how to deal with it

Poonam, your baby is a tiny 4 month old and you are right that this can later on lead to regular thumb sucking. the only thing you have to do is keep removing the finger over and over again :) there is really no other way. your baby will want to do it to try and explore, but keep repeating this and gradually he will give up :)