Well, y'learn a new thing every day...

[DanaC]

watching the programme QI, I discovered that the convention of dressing girls in pink and boys in blue is relatively modern. Up until the early twentieth century it was the opposite of that. Blue was considered the appropriate (serene and pale) colour for girls, and pink (strong and vibrant) for boys.

Also, apparently, the word 'girl' used, up until the 16th century, to refer to babies and young children generally; with 'knave girls' for male babies and 'gay girls' for female babies. The word 'boy' was a word to refer to servants.