I was on a NW airlink flight (Mesaba I think) and there was a kid who was like 2 years, 1 week. He was under 2 years when the trip started, but on his return he was over. The FA made them deplane.

I think it's odd that this would ever have to fall on the FAs at all. It seems like a total check-in/gate issue to me...but then the FA needs to enforce it also to prevent fines.

If the process is working, why should the FA ever have to check? Incase a kid with a ticket sits in a parent's lap if they didn't get seats together?