There are reasons to book the aisle & window besides "lap" kids. My husband's a big guy and I'm not too petite myself. We tend to book an aisle & window when flying together and hope the middle doesn't get filled. When arriving at the gate, I always check in with the GA and apprise them of the situation (usually pointing out DH). As long as the plane is not 100% full, the middle usually remains empty. And even if they say it is full, somehow that poor middle person stuck between us usually gets moved. Just so you know I'm not totally heartless -- if it really is 100% full, I'd rather we each take an aisle, even not together, so that no one is stuck between both of us. Makes everyone happier.