What are the appropriate ages for viewing this?

Hmm...I know that many six year-olds have watched this and have been fine. It depends on how sensitive your child is. My seven year-old sibling loves the show and has not suffered any side-effects from viewing it.

I would refer to the content advisory on here for a full run-down, but I will give you the basics:

- Season Two is much darker than Season One. There are many emotionally powerful moments that deal with separation, growing up and many plot twists are shocking and will startle viewers ("Not What He Seems" in particular!). "Northwest Mansion Mystery" and the Weirdmaggedon Trilogy are violent and the former includes brief bloody moments.

- There are some mild sexual references. Characters have crushes on other characters, one shares a kiss in "The Deep End". Many references to puberty, etc.

- There are many moments that could be considered "scary". The show is all about mystery, and this element, combined with the violence and emotional scenes could have an impact on very young children.

Overall, I'd say the average 6-year old would be fine with Season One, but check the episodes "Scary-oke", "Into The Bunker", "Soos And The Real Girl", "Northwest Mansion Mystery", "Not What He Seems", "Dipper And Mabel Vs. The Future" and the Weirdmaggedon Trilogy, they are can be quite dark at times:)

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"Do you think I've time for a snack?"

"You're always thinking about sustenance!"

"I'm not! I'm always thinking about food!"

What the guy above ^ said.

If it helps, there's the Parent Guide on IMDb, and the show is rated TV-Y7 in the United States. Of course, ratings aren't everything; most R-rated films in the US (age 17 and above, I believe?) are usually rated 14A here in Canada; it can also go the other way, as Gravity Falls is rated PG in Canada, but carries a more lenient* TV-Y7 in the US. *Canada doesn't have a TV-Y7 rating and the Canadian PG may differ from the US PG, but in the US, PG is higher than TV-Y7.

However, if your child is to properly understand and appreciate the show, personally I'd recommend at least 10. There's plenty of themes surrounding puberty and growing up that, despite being sanitized for younger audiences, are aimed directly at older children, teens and adults.

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Honestly? I'm 25 and love horror movies and there were moments in season 2 that really got under my skin, particularly in the Weirdmageddon trilogy. Bill Cipher is terrifying.

I think the best audience for this show starts at around 11 or 12, but I don't personally know any kids that watch it. Adults connect to the nostalgic, melancholy quality of the show and its excellent character writing and continuity. I wish I had this show in my life when I was in my teens. Dipper would have been my hero.

I would not show Gravity Falls to a 6 year old by any means. It's not the more adult humor (I watched Animaniacs at that age and turned out, uh, OK) so much as the frightening character models and the emotional heft. It's just too much. There are some season 1 episodes that would go over well, but once Bill shows up, Gravity Falls loses its kid friendliness.