I brought my 8 year old daughter last summer. She did great. I think she was proud to be the youngest person in the group. She never complained, and she will do so if tired and not interested. I let her take her own camera and take pictures (it had to be secured with a neck strap). She is more adventurous than me, she will go on any crazy roller coaster. So the bridge was a highlight, not a scary part. All that said, it depends on the kid. My son is 6, and I will not even consider taking him on this tour at age 8.
The first half is walking, the second half is a bit more relaxing. We did do an 8am tour, which meant getting up really early, but there were only 7 people in our group, so that meant less waiting around.