We had a great time. In this case "we" is me, my wife, my 10 yr old, and my 6 yr old. We only did Sunday as this was my youngest's first con and I wasn't sure how it would go.
First, you couldn't throw a d20 without hitting an enforcer. They were EVERYWHERE! And they were all, every one we met, helpful and friendly. This removed a lot of stress as we didn't feel as lost or helpless as we might have otherwise. At one point me and one kid split off to go to an event and the plan was for the other two to join us in a short while. Oops! We forgot to say where we were going or how to get there. No problem, the nearest enforcer knew exactly. This was my first PAX and I read so much from the PA guys about how amazing the enforcers are and it is not hyperbole.
The venue was appropriately sized. It felt like there was plenty to do and see and tons of people to play with, but without feeling crowded or oppressive. I love GenCon but there's so many people in that space you can't move quickly when you need to and sometimes you can't even move slowly.
The app... let's just say I never figured it out. The schedule seemed to work fine. The messaging system worked sporadically. I never got replies to any of my posts. I never figured out how "connections" work or what "checked-in" means. Having the map in there was nice.
I've been going to GenCon for years and the one thing I don't get there I always wanted is random pick-up games with strangers. And the lending library prices at GenCon are a real turn-off. The open play area at PAX was a dream come true for me. Big library of games. Hundreds of people looking for other people to play with. Free. I could easily spend 75% of a whole weekend in this section, with the remaining time split between shopping and eating. PAX Unplugged, in my own words, is a board game night that lasts for 3 straight days and has thousands of people. That is definitely something I want in my life.
So I don't know what the other days were like, but Sunday was definitely kid friendly. Lots of dealers had kid-friends games for them to demo. We bought two and made notes on many more for future purchases. We missed the 10am kids games event (it was full), but an enforcer alerted me to the 3pm one and both kids had a great time.
One of the things I love about GenCon is feeling that comfort of being amongst "my people". Somehow it was even moreso at PAX. Looking around at thousands of people and thinking, "These are all boardgamers!" was electrifying.
As a final data point... I've been going to GenCon for 14 years and I've never made a friend there. I made a friend at PAX. That's noteworthy.