I'm failing to understand this. You're travelling during the holidays, which means the flights are going to be full. Aside from the issue of not getting your AC/DF seating (open B or E seat), what makes you think that the middle seat would stay open? If taken, then are you going to keep a stranger in between the both of you? If not, then you're in the same position as you are right now. And if you really wanted that open middle seat, why not buy the seat for your 20 month old, which you will have to do anyways in 4 months. This is not intended to be rude, just understanding where you're coming from.