For fans of old movies this musical from 1944 should be pretty well known. The light hearted story is based on life of an actual family of Smiths in St. Louis, with a small plot around a love affair of Esther (22-year-old Judy Garland) with a young man next door. While Judy did some acting when younger, the relevant actresses are Joan as Rose, and especially Margaret as her little sister "Tootie."

Margaret's acting is limited by the genre, and the style of the period, but in my opinion she's one of the most interesting young actresses before 1970s. Margaret received an Academy Juvenile Award for the role, which Wikipedia cites as her most memorable one. If you're into old movies, this is a must-see, and for the average visitor of this site, a good choice if you're only going to watch one movie from 1940s.