Parents who want to lift their kids in a gender-nonconforming way have a new stocking stuffer this yr: the gender-impartial doll. Announced in September, Mattel’s new line of gender-impartial humanoid dolls don’t clearly identify as either a boy or a girl. The dolls come with a variety of wardrobe choices and could be dressed in various lengths of hair and clothing kinds. But can a doll—or the rising...