Among other babies, I have only seen them thumbsucking. But my 3-month old baby tends to suck his index finger!
Believe it or not, he does. When he was just 2 months old, he first attempted to put in his entire hand in his mouth. Of course, that was just impossible so he just ended up being frustrated until he discovered he could actually put the full length of his pointer finger.

At first, everyone thought it was hilarious. But soon enough, we are in panic because there had been several ocassions when my baby vomits (not just possets) while sucking his index finger. Apparently, he reaches out too far to his throat (That's what I think since he makes that really loud gagging noise).

Now, it seems pointless to scold my baby at this age but I'm afraid that if he keeps on doing it, he would just end up vomitting every other time. I am considering to find a way to really stop this budding habit but I also heard that thumbsucking (well, in this case, index finger-sucking) is important for babies to help soothe themselves even in the caretaker's absence.

What should I do? If I am going to train him not to do it, how can I exactly do it? It's driving me nuts when he gags and vomits all of what he just drank.