Baby sucking hands!

Yes, it’s very very common. In fact many babies do suck their thumb or fingers at any point of their lives, some did them when they were bigger but mostly did that when they were infants & toddlers. It does becomes a habit if adults don’t try to change them slowly and it takes some time to do this, so pls be patient with this new habit. Usually the sucking actions make them feel comfy and soothing enough to calm themselves to be quiet and can nap much easily. My own kid sucked her thumb for about 6 to 8 months and has stopped by herself when she turned 1 year old plus.