In a very similar position to you in that am thinking of taking my newly-teenage daughter whose keen to go. I on the other hand fear slipping into some kinda discontented nostalgia should we attend
Also went in '84, in fact it was my first festi

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Last time went to the stones at solstice though was '89 I think, proper cat-and-mouse games with the cops and the army and we ended up celebrating/partying for two days on a mile-long track with a stage mocked up in the middle about a mile from Stonehenge.
If you go with even the slightest idea that it's gonna be anything like it was in '84 then you'll be disappointed. If you go along without preconceptions you just might have a magical time with your lad
I'm reliably informed that plenty of good crew still attend , along with all sorts of others just along for the craic, a smattering of druids, a few pissheads etc and still quite a few of that odd cult who wear the freaky pointy blue hats... (you know, the ones who really wanted the place to themselves that much that they used to ring the place and try to exclude everyone else)
As has been said, Avebury is a much more chilled vibe, and there are many other sites where people gather, depends what you're after.