Yabu.
I went to Glastonbury quite a few times as a child, it was fantastic! The kid's field was lots of fun, but we went to watch acts at the pyramid stage aswell and it was fab, I remember sitting on some random guest shoulders watching the cure, I was about 5. We also went to see Sinead O'Connor and van Morrison.
It was lots of fun going to Glastonbury as a teenager, I had quite alot of freedom but it was nice to have my mum there.
Lots of my mums and their kids went to Glastonbury so there was always a little gang of us, we were left in the kids field sometimes and we just stayed up late watching bands.
Yes there was swearing, drinking and some herbal cigarettes drugs but there was no aggression or drama, it was a lovely atmosphere.
It is up to the parents what they choose to do with their children, all the children I grew up with have turned into relatively normal adults despite being taken to festivals.
Glastonbury is a pretty tame festival, we also used to go to nudist/crystal healing festivals, I wouldn't choose to take my child to them but I would take him to Glastonbury.