Years ago I was seated with my then 5 year old son in the exit aisle. The ticket counter did that. And yes they noticed the kid and that he was in fact a minor kid.

When the air line personal noticed that they stopped the flight and it got delayed.

There where not any seats next to each other left.
And the son needed a grown up next to him.
They asked several [people including an elderly couple. They all said no. I understant that. Who wants to be responsible for a kid and a kid you dont know.

Finally the stewardes had to give up their seats and we could take off.
In between people were pretty pissed of at me.