In America we call this a “onesie,” but on our recent Europe/UK tour we learned that Brits refer to it as a “grow,” as in, “Say, what a good baby grow.” The first few times we heard it, we thought people were saying “baby *girl*,” because of how funny British accents sound to us. Needless to say, we were baffled that people were referring to this gender-neutral clothing item as a “girl.” Anyway, the fault was, we now admit, ours.
This thing comes in two sizes: 6-12 months, and 12-18 months, which is how baby sizes work. Strange, right? Those aren’t sizes, they’re units time. It seems like the closer you trace life back to birth, the weirder things get.