You might be surprised at what children will listen to, enjoy and understand, so long as they are not told that it's 'hard'. For a long time I used the noisiest bits of 'The Rite of Spring' as a basis for a Yr 7 (age 11) composition project.
Comments after first hearing included,
'That's really scary. I like it'.
'Was that from "Jaws"?'
'That can't be right. Cavemen didn't have violins.'