RE: Kids. The shows are 'all ages'. Having said that, a few thoughts:
I will be honest...until they're teens I can't justify bringing a young kid into the general GA pit. There's just too much that can happen, as did when I brought my 10 year old.
Mind you, IF you get into a controlled elllipse/heart like environment, it is awesome for them as the crowds there are respectful and even when there's a surge it's far less dangerous imo.
The other thing - and it's a HUGE thing - is their hearing. I saw kids without ear plugs on the Vertigo tour and to me thats as bad as letting them ride without a seatbelt on - actually even worse. They WILL get hearing loss, absolutely. It is the main reason why my daughter (9) and I decided she will not come this time around. She is very musical and has a very good ear, plays piano, and she felt it was a risk she didn't want to take. Yes, there are earplugs she could wear but the good ones are very expensive and the cheap ones block out so much sound she just thought it wasn't worth bothering just to see some lights and the band. "I'll watch the DVD", she said. She's 9 going on 29. lol.
Speaking of the lights/visuals...U2 is known for it's intense light and visual presentation. This can have a detrimental effect on some kids, particularly those prone to seizures or afraid of bright lights. It can be physically exhausting for them and you may find them wanting to leave before the show is over and you wanting to stay.
Anyways, I will be bringing my 14 y/o and for every precautionary tale I'm sure there are 10 or more glowing tales about how GA was ok with their kids. That's cool, only a parent can know what's best for their own kid and what they're able to handle. If I had to do it again with my guy when he was 10, I'd have taken him to decent seats at that age, and GA now. Even back then, as much into basketball and soccer as he was, he got really tired out and I wouldn't say that that and the rude people "ruined" it for him and us, but it came pretty close. Contrast that with me taking him to see The Police from decent seats - that was way better for him and he has nothing but great memories from that show. His memories from the U2 show, sadly, aren't all that positive, which I'm disappointed about because of course I was hoping he'd be awed and love every second of it. The good news is, he knows alot of that is because of how young he was and wants to go again, so thats cool I guess!