Hey kids, life is just gonna get tougher you know...
This film is amazing, but for myself (and many others around my age...i'm 28) it was the first inkling that you know what...Life isn't going to be a walk in the park (with jumpers for goalposts) all the time.
Even as a nipper, watching the end sequence as the camera pulls away from James (it's written on his scarf eagle eyed fans!) as he stand alone, his true friend that has just disappeared, never to return again, i started to think 'Okay, maybe those Disney films have lied to me. Life IS going to suck.'
Then i put on Watership Down and confirmed it.
Which is why it's amazing (as is Watership Down) as they don't talk down to children. They touch subjects like death, loss and rabbits caught in snare traps coughing up blood as the flies start to swarm sensing death looming...sorry, had a flashback there...!