'A Doll For Everyone': Meet Mattel's Gender-Neutral Doll

A child opens a box. He starts jumping and screaming with joy—not an unusual sound in the halls of Mattel’s headquarters where researchers test new toys. But this particular toy is a doll, and it’s rare for parents to bring boys into these research groups to play with dolls. It’s rarer still for a boy to immediately attach himself to one the way Shi’a just did.

An 8-year-old who considers himself gender fluid and whose favorite color is black one week, pink the next, Shi’a sometimes plays with his younger...