I took DSS 10 and his friend to see Guardians of the Galaxy. It's rated 12A and, having watched other Marvel films of the same rating I knew it would be fine for DSS and his friend to watch it.
The trailers before the film started were completely inappropriate, however! The first was for Sin City 2, which is an 18 - granted it probably didn't look very exciting to DSS and his friend. The second was for Let's be Cops, 15 rating - DSS and friend "haha that looks really funny, we want to see that" no as it's too old for you. And finally a trailer for Sex Tape! Completely inappropriate!
I emailed the cinema and explained this to them and the reply I received said, all the trailers featured 12A content so were fine.
Am I being unreasonable to think that just because you show the potted version of the 15/18 rated films doesn't mean they are fit to be shown before a film rated 12A?