The EF seat map usually shows "X" for seats that are blocked from selection. In this case, 23B is showing occupied. I'm more inclined to believe someone was assigned the seat between your wife and you.
You can keep moving around the cabin to other trios of seats and hope someone else doesn't grab the seat between you two.
I realize it's a cost savings, but for such a long flight with a 2 year old it would seem prudent to buy the additional seat than roll the dice that you'll have an open flight with the unused seats.