Breeching
veronica_rich suggested I post this costuming information here. It's something we don't think about too often, but I visited the Huntington Library twice in the last week, and this picture reminded me of the fact that young boys wore "shortcoats" (which looked pretty much the same as girls' dresses) back in PotC times, until they were 7 or so, although the exact age at which they were "breeched" was a matter left up to their parents.
Here's another picture from the mid-1700's, which I found with this great article on the subject at Wikipedia -- that site gets better all the time!
I was researching the subject for a drabble I wanted to write, Rite of Passage, for the 'Fly' theme at blackpearlsails. Jack and little kids are always fun together.