This is all such helpful info. Yes, we are flying Southwest. We do have young children. However, I was told on another board that sometimes when the flights are full of children, they don't allow families with young children to board early, as most of the plane would be pre-boarding! That's why I was trying to get that coveted "A" boarding pass early!
I hadn't heard that Southwest was allowing 24 hour checkin. Yep, I just checked the website, and sure enough, it now says 24 hours ahead of time! That's great! No trekking down after midnight!