Not quite a festival,but: When we ran a non-alcoholic St. Patrick's day type mini-celtic concert, we wanted to encourage people to bring families. We set up a single adult rate, lap-sized kids free (we were not outdoors, so seats are valuable real estate), half price for older kids and seniors; and, a family rate so families with more than two kids could bring them all with a blanket admission. We didn't have a place parents could park their kids, we pretty much expected them to supervise their own. No problems to speak of. Kids can't learn to behave at public performances if no one takes them in the first place (they should also be willing to take them out if they misbehave). This was not a weekend event, but just one night of two or so hours. One family called and asked about the family rate, turns out four adult children brought their parents. We didn't specify otherwise and didn't fuss about that either.