Based on Sans Famille by Hector Malot.

This is a faithful if compressed adaptation, telling the story of Remi who is sold off to Vitalis the travelling musician and his band of performing animals. It has musical numbers typical this era of Toei films, some awkward slapstic, plenty of scenes tailored to pull on the heartstrings, and very smooth animation. Overall a pleasant film that's interesting to watch for the technical aspects; but the story leaves much to be desired, being on the melodramatic-maudlin side. The later Dezaki/Sugino version is very different, with 52 episodes for the story to breathe in and far more compelling storytelling.

(Source: AniDB)