Jurassic Park for me. I had an amazing JP jumper when I was like...maybe 6. It was far too big for me but I loved dinosaurs. Naturally this meant I wanted to watch the film because...well I'm 6 and it's got dinosaurs.
Ultimately I ended up watching it with my Mum and Dad. We got as far as the iconic T-Rex chase scene and I told them to turn it off. Didn't go near the film for another few years.
I've now got my own 6 year old. There's no scenario I could envisage where I even consider letting her watch a film as gory, tense and frightening as JP.
I watched Jurassic Park when I was like 6 and absolutely loved it. Little Nemo Adventures in Slumber land however absolutely terrified me at about the same age.