You pick out a girls’ size 6 short-sleeved shirt and shorts for her and a boys’ size 6 short-sleeved shirt and shorts for him. His fits perfectly. Hers doesn’t even come close.

How did we end up with two "teams"--boys in blue and girls in pink? "It's really a story of what happened to neutral clothing," says Paoletti, who has explored the meaning of children's clothing ...