In reply to deepsoup:
What sort of camp is it....? IS it one where the parents (primarily) are expecting the young people will be taking part in adventurous type activities. If that is the case then they will have already signed a form saying they give their permission for their child to take part in these activities and slacklining... if an activity ok'd by the camp organisers would fit this bill.
If it is a camp where they are making music and sticking leaves on a collage you may need a permission form.
Which ever a RA is definitely required.