“First Snow” is a live, kid-focused performance now playing at L’Alliance New York, the city’s long-running home for French language and culture. Set around the arrival of winter’s first snowfall, it uses stage action and sound to trace how children notice change in the world and in each other. In a city where weather is shared public drama, the piece treats a small seasonal moment as a lesson in attention. It lands as quietly observant rather than noisy.