You have been very, very lucky then. I always arrive at the airport early and sit in one of those seats right next to the desk. Every single flight, without exception, I've seen at least a couple of families raising heck with the person at the desk, demanding that other people be moved, so they can sit next to their young child. They are always told that there is nothing they can do and that they had the option to purchase their seats and chose not to. The response is always the same (almost word for word), "No we didn't purchase seats. We didn't dream Air Tran would separate us from our kids, so we didn't think we needed to. Now you have to move someone so we can sit next to our child". The response from Air Tran is always the same. 'Ask when you get on, but we can't make anyone move if they choose not to'.
Another problem with not purchasing seats is that most of the flights I've been on have been oversold. In fact, every single Air Tran flight I've been on this entire year has been oversold. The people that didn't purchase seats are the ones to get bumped if they can't find enough people willing to voluntarily give up their seats for one on a later flight. This past October we saw security called when a man was having a screaming fit because he was being bumped. Security told him he could either calm down or he could leave the airport. He yelled that he didn't know that just because he didn't purchase a seat that he'd be one of those bumped. He finally calmed down and hopefully got a seat on a later flight. I fly solo alot, but still purchase my seat. Due to claustrophobic issues I don't like the back of the plane, nor do I like middle or window seats, nor do I want to be bumped to another flight, plus I want to know that there's enough room in the overhead for my carryon, so I pay for the more expensive $15.00 seats that are toward the front of the plane. I get my preferred aisle seat that I need and am in boarding zone 1. It's just an extra $30.00 that I count into the price of the flight. Almost every flight I am asked to give that seat up for some middle seat in the back of the plane for some couple or parent who chose not to pay for their seats. Sorry, not happening!