Just asked dd (16yrs) for advice as she's been to lots of concerts there. She suggested that you all meet in the main foyer underneath the light installation which she says you can't miss. She said that most people then walk to the tube station beside the O2 and whilst it's busy, they manage the crowds well.
After the concert there are streams of people coming out and the restaurants at the bottom can be busy and crowded so I'd aim to meet them somewhere near the main exit after they've passed through that part. Then its a really quick walk to the tube. I am rubbish at directions so can't give you a spot to meet although I have a memory of a ticket dest as you go in on the right.
but I would say that when I have been its very convenient to get the tube as its near to the venue and we got away very quickly and easily. I would only meet them if they were particularly nervous/young as its well lit with plenty of people around.
My daughter is going to concert at the o2 with friends. They are going to travel up but I am going to meet them to travel home as feel uneasy about them travelling around in London late at night. I have never been to the O2. Does anyone have any advice as to where would be a good place to meet them, or as to how chaotic (or otherwise)is at the end of concerts there? Thanks.