The family with the car seat had boarded before us. The car seat was in position in the middle seat when we got on the plane. DD, then 12, isn't exactly "small", but I didn't notice her having problems getting by the car seat.
There are 5 in our party, so I book us in three rows 2-1-2, so each kid has a window seat.
The family with the car seat offered to swap so their DH could sit in DD's window seat and DD could have his aisle seat (next to me). We declined. Of course, I could have raised the issue and had DD move. I elected not to. But again, FA's said NOTHING about it, not even asking us if we wanted DD to move. So in my opinion, it is false to say the plane can't move unless the car seat is in the correct spot. Because it can, and does.