I agree with you about the over 18 rule, here at the Wath festival we have a full day (Mayday) specially for kids with maypole, clowns, dances, laughing policeman, jugglers etc. I don't know the reason for the over 18 rule but Butlins may have a good reason, why don't you ask them? If you feel that bad about the rule then I can support your stance on not attending, but it's a sell-out concert so I can't see that changing the rule. Contact them, make your concerns known to them.
I did notice that all the play area's were closed, maybe it would cost too much for the staffing of these areas, and at this time of year they would probably be empty majority of the weekend.

Ha Ha, not sure about the old age gits, I'm certainly and old git but I did see some young people there, lot's of them actually but over 18 of course. I can remember my grandparents taking me and it was always freezing cold. Hence my favourite song of John Connolly "Out of Season".

Keep your fingers crossed this old git is still alive for the next one seeing that I have tickets for it.

Whoooop Whoooop bring it on............................