you see toddler girls with very short hair as a Style sometimes in the 19th century and into the early 20th, but yeah, not as much for 9-year-olds in 1904 (100 years earlier it had been a popular look for adult women and little girls alike, but that's a very different era)
although I will say, one of the twins' socks are too short in the newer illustration- the long black stockings in the original are more accurate. people also REALLY like giving kids light and/or bright-colored play clothes in eras where the Laundry Realities made that much less popular than darker shades and small prints that wouldn't show stains as easily
Samantha's play dress is a great example of this:
(the pinafores were easily bleached/boil-washed and therefore were a practical choice to protect an active little girl's dress)
it's not that it NEVER happened, of course. and it's hard to find truly candid images of children from this time, as in images where their parents didn't dress them specially to be photographed or filmed. but you can see a lot of dark or deep-colored dresses (some under pinafores) in this still from a video of children leaving St. Ignatius' School in Preston, England in 1904:
I feel like putting the twins in light or bright aqua on a random, ordinary day is, while not impossible, a bit unrealistic. very I Live In An Era With Washing Machines And Machine-Washable Fabric