They will probably be able to help you at the counter at the airport, I would get there early. On a trip last year, we were "mysteriously" bumped out of our seats, they could not figure out what happened (so they said). When were on the plane, I noticed a couple with a young child sitting in them. I wouldn't be surprised if someone moved us to accomodate them. I'm glad that the family got to sit together, but I didn't appreciate being involuntarily bumped out of the seats I had reserved months before and reconfirmed a couple days before leaving. I have also seen flight attendants asking people to move after boarding to get families together. On our last flight they asked at the gate if there were 2 adults sitting together who would like to move to the exit row so that a family could sit together, a couple volunteered