Call it a coming-of-age: several leading children’s museums have recently expanded, all while serving as models of environmental stewardship. Brooklyn Children’s Museum, the nation’s first for kids, sports a new canary-yellow, Rafael Viñoly–designed upper level incorporating solar panels, and has display cases made of compressed sunflower seeds. See the just-unveiled permanent exhibit on Brooklyn’s natural habitats (yes, New York City’s most populous borough has woodlands and ocean tide pools). Boston Children’s Museum acquired a striking glass-walled extension with a light-up dance floor and a three-story vertical maze—plus rooftop gardens and a storm-water reclamation system that earned it LEED certification. San Diego’s art-minded New Children’s Museum (619/ 233-8792; thinkplaycreate.org), built from the ground up, has studio space where kids can decorate a 1973 VW Bug. And in October, Philadelphia’s Please Touch Museum (215/963-0667; pleasetouchmuseum.org) reopens with triple the space after a move to the Beaux Arts Memorial Hall. Among the additions: a 40-foot replica of the Statue of Liberty’s arm and torch—a nod to Philly’s hand in building Lady Liberty’s pedestal—and a 1924 Dentzel carousel in a pavilion next door. Sure beats Mom’s lecture on Impressionism.