My kid could watch Robo Cop and not flinch. She is a hard little monster.
She really, really, really wants to watch scarier horror movies. She loves Goosebumps, Beetlejuice and Coraline and knows that there are way scarier things that she would love to consume. For the life of me I can't think of many 'safe' horror movies for her at age 6. We watched Army of Darkness, which she declared was the best movie ever, and Night of the Living Dead. Wish I could think of others that aren't too horrible or sexual, maybe the Dark Crystal, it gave me nightmares as a kid but I think she would eat it up. Personally neither me or the wife are horror fans.
As an aside, I think my kid might watch and hour or two of YouTube a week on average. It's not a big passion of hers.