They're the same brand, same size (according to the labels).
One is purple with polkadot bats, very stylized, on it.
One is white with black spiderwebs and spiders, rather more realistic, on it.
Guess which one is "boys" and which one is "girls".
Anyway, hanging up laundry today, I noticed the purple one is simply smaller. I double checked the sizes. Yep, same label size, same brand. Sadly, I am not at all surprised.
I put the two shirts together, and the sleeves, the headholes, and the lengths were almost identical. But the shirt from the "boys" section was wider, with much wider sleeves.
My conclusion is that kids clothing designers think that girls should be wearing tighter clothing than boys. And apparently, girls should start to be shamed by their clothing size labels as early as possible. (Remember the "does this diaper make my butt look big?" baby onsie? A six-year-old daughter of a friend has been asking her "Am I fat?" because said daughter wears "husky" sizes.) And differences between the sexes (sizes, shapes) should be anticipated by gendered clothing several years before puberty actually starts to cause those differences. (Warning: now I'm starting to get really tongue-in-cheek) Because if little boys and little girls wear clothing that is too similar, then, um, someone might use a wrong pronoun? Horror! Worse yet, what would happen if children grew up realizing they have plenty of things in common with the opposite gender? Would no child grow up to be heterosexual any more!?