Unless there was some traumatic birth event or some karmic reason, all children are born energetically open: chakras, meridians, etc. I would bet that most children are born with their third eye open.
(AND having an "open" third eye does not mean you have super woo-woo psychic powers. Seeking to "open" your third eye does not make you more psychically in-tune. Chakras are a part of your anatomy - people ascribe certain extra powers or emotions to them, but that is not the end-all-be-all around chakras. It is like saying having large feet make you a better athelete - perhaps yes, perhaps no.)