Obviously I don't mean it's unsuitable for children. I just mean that the protagonist (and also the hero, i guess) isn't a sickeningly sweet damsel in distress looking for a prince. Rather, the main relationship in this film is between two sisters- one who must combat her inner turmoil each day and stay locked away because of her powers- and the other, who has been shut out and feels lost and abandoned by her older sister. Yes, yes, there are love songs and handsome men in the film but the focus is the sisters.
As an added bonus- here is an awesome trailer showing what Frozen would be like if it was a horror movie. This just shows the power of editing! This isn't the first time that careful editing and music has been used to bend the genre of a movie. It has been seen on youtube in trailer remakes of Mary Poppins and the Shining, but this one may be my new favorite. "Do you want to build a snow maaaaan?"