Husband and I flying with 11 month old from PVD to MCO with our lap child. I'm Mosaic so we're in the EMS seats already. We booked an aisle/window hoping for an empty middle seat (but are fine if not, so no problem there). My question: on the day of departure if the seat is still showing as open, is there any way for the gate agent to block it for us once we arrive at the airpot, or do we just take our chances once everyone has boarded?

And yes, I know the only way to guarantee a seat is to purchase one, I'm just curious of our chances.