We rented this and I naively thought that a Barbie movie would be safe for my kids to watch, at least in terms of not scaring them. I was wrong, and we ended up turning it off halfway through because my kids (3.5yo and 5.5yo) were both crying and telling me they didn't want to watch anymore. And they consider movies to be really fun treats, so this is really saying something.
There's a scene where the girls' house burns down, and several scenes with a scary villain and her dragon. I think it was the dragon that put my kids over the edge.