Yesterday, February 12, would have been my mother's 90th birthday. In her memory, I decided take a close look at children's fashion in the year of her birth. As the third child born to a young German Lutheran minister and his wife in rural Canada, I doubt if she ever wore any of the fancier styles shown here, but family photos certainly confirm the rules of appropriate clothing for children under 7.
Babies from birth to around 6 months: long white gowns, ranging from minimally embellished to elaborately trimmed with lace and embroidery.
Babies from six months to a year or slightly older: short white dresses and one-piece rompers. Again, these could be plain or fancy, depending on the occasion and the family's budget and needlework talents.
Gender differences were introduced between one and two years, with little boys exchanging dresses for short trousers, often attached to their shirts or blouses with buttons at the waistline. Little girls stayed in dresses, but in an array of colors.
Here's a video I created for the occasion:
Ever hear of
Amelia Bloomer? She was the American writer and activist who attempted to reform women's fashions in the 1850s by advocating -- and wearing -- knee-length dresses with full matching trousers underneath. She and other dress reformers called it "the American costume", to differentiate it from French-influences fashions, but the popular name "bloomers" stuck. The idea of women wearing any form of trousers was ridiculed and roundly rejected, but bloomers became acceptable for athletic costume, as long as they were worn in public.
Fast forward to the 1890s, when bicycles were the latest craze, and young women traded flowing dresses for divided skirts, bloomers and even their brothers' knickers in order to enjoy the new pastime. Once again, the cartoonists and editorial writers had a field day, but this time practicality won out.

creeping apron, 1908
At the same time, a quiet revolution was taking place in children's clothing. Some unknown enterprising person -- probably a mother -- had the brilliant idea of sewing up the hem of her baby's dress, leaving only two holes for the legs. The resulting "creeping apron" (later shortened to "creeper") was initially worn over another dress, like a pinafore, but by the 1910s was worn by itself.
A more fitted version, the romper, was introduced for toddlers. Physicians and advice manual writers praised these outfits as being ideal for both boys and girls.
In contrast to the reception of trousers for women, the idea of putting little girls in creepers and rompers met with apparently universal approval. There were no anti-romper cartoons, no editorials decrying the masculinization of girls. According to the baby books and paper dolls I have seen, rompers replaced white dresses as the preferred neutral option for toddlers very swiftly, between 1910 and 1920. I say "neutral" because until the 1930s, gender-specific version of either garments were very rare. (Yes, boys wore
pink rompers.)

McCall Magazine illustration of a romper and a creeper, 1920.