I saw the film years ago on an English language promotional preview DVD from Central Park Media, which has been out of business for a couple of years now. It's a fantastic film, but my opinion is that it's definitely suitable only for children that are at least 10 to 12 years old. The subject matter -- siblings struggling to survive in the horror that was Japan as World War II ended -- is way too serious and disturbing for those younger than that.
Here's what Sentai has to say about their upcoming release:
GRAVE OF THE FIREFLIES has been universally hailed as both an artistic and emotional tour de force, with famed critic Roger Ebert calling the feature “An emotional experience so powerful that it forces a rethinking of animation” and stating that “it belongs on any list of the greatest war films ever made.” Sentai Filmworks is extraordinarily honored to have been given the privilege of handling the digitally restored version of one of the art of animation’s true crowning achievements.