When you are a design critic and a new parent, your first encounter with much of baby world leads to many questions. Why does every toy come in three primary colors, rather than a single hue? Why so bulbous? Why does it need to light up/sing “Old McDonald”/moo? My first encounter with the expanded Brooklyn Children’s Museum, which reopened in Crown Heights this September, made me ask almost the same questions—and with the same fear of being a spoilsport.