Top child radical — pictograph of a swaddled infant, head and outstretched arms above, body wrapped below. The indexing radical here, supplying the meaning:
孟 originally meant 'eldest child / firstborn son', then 'first month of a season' (
孟春 first spring,
孟夏 first summer), and finally became a surname carried most famously by the philosopher
孟子 Mencius.
