In the early 1900s, children's fashion was undergoing a lot of changes to accommodate active children. While girls and boys had their own separate fashions, a few similarities existed between the two genders. If you know what to look for and expect, recognising clothing from this time period is fairly easy.
"Historical Boy's Clothing" reports that kids' clothes in the early 1900s were heavily starched and looked formal compared to modern kids' clothing. Clothing was, however, becoming looser and easier to play in, compared to previous decades. Both boys and girls sometimes wore sailor suits during more formal settings, and sometimes similarly formal dresses for boys as well as girls. Colours were generally pale, ranging from browns to whites. Clothing was getting shorter, with children generally wearing longer socks and black shoes, according to an article published by the Dakota State Campus School.
Fashion for girls largely mimicked those of their mothers, decorated with lace frills and ruffles, which would be heavily starched. Under the dress, long black socks covered any exposed skin. Some parents would make their own clothing using patterns from companies like McCall's, as recorded in "Costume Gallery," which featured tucked stitches. On some patterns a deep "V" appeared on the front and back, showing some of the blouse underneath. Later patterns also featured a single panel of fabric running the whole length of the dress.
Boys in the 1900s wore tunics and Russian blouses, both of which offered freedom of motion. In addition, boys usually wore knee shorts or knickers, which exposed some skin below the knee, until reaching their high socks. Younger boys also had romper suits, one-piece garments which were designed for play, as described by "Historical Boy's Clothing," an article on the subject. Caps and stockings were acceptable with rompers, but less so with other garments. In formal settings, boys would wear suits with Eton collars, or sometimes Fauntleroy suits, although their popularity was waning.
During the 1900s, clothing was made of flannel, linen, wool, silk, muslin and cotton; the cotton, muslin and linen were often starched heavily. According to "Historical Boy's Clothing," wool was typically used in more formal clothing. Starched material takes on a stiff quality, which can be uncomfortable for children because it restricts their range of motion. Elastic was also a new addition to clothing, allowing for more flexibility. Zippers did not yet exist, so clothing was held together with buttons.