Céline Sciamma’s “Portrait of a Lady on Fire” was my favorite film of 2019, but I was still unprepared for what a gentle gem her follow-up, “Petite Maman,” would be. In just 72 minutes, Sciamma composes a spare but enormously rich fairy tale about an 8-year-old girl who, in a time of grief, meets another girl mysteriously similar to her in the woods. There’s a magic here that Maurice Sendak would have adored.

