By googling BGG I quickly found the following important information about BGG:
Q - At what age can teenagers come to BGG unaccompanied?
A - Sixteen upwards. At sixteen or seventeen you are responsible for yourself but can not be wholly responsible for children - including teens 13 to 15 (!).
Q - Are there shower facilities?
A - Yes, solar showers.
Q - Are there proper flushable toilets or hole in the ground type loos?
A - There will be poly john loos. There will be no holes in the ground.
Q - Will there be instruments, bongos etc on sale at the event to save me bringing mine - as I would like to buy another one down there?
A - Yep, loads of instruments to buy but we cannot guarantee you'll find what you're looking for as this is all in the hands of the vendors.
and more... http://www.big-green-gathering.com