Children's fashion, much like fashion for adults, evolves due to the changes in the world. In the 1930s and 1940s children's clothes saw a change from drab, monochromatic colours and natural fabrics to more colourful, patterned looks with some decorative touches. However, some parts of older customs such as practicality and proper body coverage were maintained.
The materials for all clothing, including children's clothing, changed between the 1930s and the 1940s. There was less home sewing on the whole as more clothes were bought from catalogues and stores, pre-made and ready to wear. Due to the shortages of materials because of the war effort, wool, silk and other natural materials were used less in favour of materials like rayon and nylon, which could be produced more cheaply.
For girls the transition period from the 1930s to the 1940s resulted in some notable fashion changes. Dresses were still popular for girls, but in the 1930s they'd been mostly in sombre, uniform colours with straight lines and simple cuts. Heading into the 1940s there were more ruffles on girls' dresses, particularly at the hem and on the shoulders. For older girls ruffles were also at the neck and bust lines. Thanks to industrialisation, patterns became more common as well.
A hat was considered to be a necessary part of any outfit. Children were more exempt from this than adults, but children still had to wear hats in any formal situation as well as many casual occasions. Caps were common for boys until they were old enough to wear a man's suit. Girls often had miniaturised versions of ladies' hats and bonnets. As the fashions of the 1940s took hold, head wear for women in general was less and less a part of their attire.
A constant throughout both the 1930s and the 1940s was the practicality of clothing. While fancy dresses might have a few ruffles and some lace, they were never garments that were truly restrictive. The same was true for boys' clothes, which were meant to cover and fit. It was a reflection of the trend in adult clothes, which were practical and which had no time or concern for frippery that would waste materials better used on other projects.