The 2YO Doll is an item in Momodora I.
Like almost every item in Momodora I, the 2YO Doll is just a collectible item, with no real effect ingame. To obtain it, press the F12 button on your keyboard three times. The hint to obtain this item can be found within the game's folder which states the following: (momodora/data/doll/press_f12_three_times.txt).
After pressing the button thrice, the item just appears in your inventory.