Studio Ghibli's Ponyo on the Cliff by the Sea, which was released just last year became very popular not just among kids only but also Hayao Miyazaki's fans of all ages. Inspired by Hans Christian Andersen's The Little Mermaid, the plot revolves around a goldfish named Ponyo who befriends a human boy, and wants to become a human grrl.
I have to admit I have not had the chance to watch it myself, but it comes recommended, and have won multiple awards both in Japan and internationally. The theme song is so catchy you can't help but sing along with it.
BUT I found one of the voices behind the theme song, Fujioka Fujimaki and a very cute Nozomi Ōhashi, who is only eight years old.