My Ex wants to take my DS and his friend to a festival this summer. He hasn't asked me directly, just told DS he's doing it and said to him that it's just a small festival. I think Ex and his GF were planning on going anyway and it coincided with the weekend he asked to have him.
I don't know what kind of festival, but I had a look and it didn't seem particularly family friendly, it's not huge, but a rock music kind of event.
I'm always a bit nervous of festivals and teenagers, personally I don't think that they are a good mix, even some of the smaller ones, apart from the ones specifically for kids.
The parents I've known who bring theirs tend to let the kids wander on their own in the evenings, feeling that they will be perfectly safe but really having no idea where they are, limited phone contact, and around a lot of drinking.
Teenagers are by nature wanting to experiment, but in a crowd at a rock concert at 13 at night at night? I'd just rather they went when they were over 18.