Kathy Culbert owns this carte de visite captioned "Dora and Frank" and is having trouble dating it.
Children's clothing can be confusing. Mothers often dressed boys like girls until they were school age, but you can tell the difference by their hair. Girls had center parts; boys had side parts.
Here, the boy (on the right) wears knickerbocker-style pants, high laced boots and an upswept hairstyle from the 1860s. The big curl in the center of his head was actually the fashion.
His sister's dress has a ruffled yoked bodice and bows along the hemline. She also wears high boots. Girls' attire mimicked that of adult women, so compare it to dresses in books such as Dressed for the Photographer
by Joan Severa (Kent State University Press, $65).
A good source for dating kids' clothing is JoAnne Olian's Children's Fashions 1860-1912
(Dover, $12.95). It features fashion plates from the 19th-century magazine La Mode Illustree
. Designs similar to these outfits appear in plates from 1867.
The rest of the details in this image confirm this date. Photos were taxed from Aug. 1, 1864 to Aug. 1, 1866. The lack of a tax stamp on the back of this photo means it was taken earlier or later than those years. The girl's clothing is evidence for post-1866. The double gold-line border dates it to between 1861 and 1869.
Culbert can verify the identities of Dora and Frank by studying her family tree for children of these names during the late 1860s. I'd estimate their ages here as 6 and 4, based on their attire and face shapes. Frank, especially, still has a round baby face.
By the way, the kids' stiff stances aren't due to nerves. Look at their feet. Braces, barely visible behind these children, clasp them around their waists. Photographers often used braces to keep fidgety children still.