According to her autobiography, Laura Ingalls Wilder learned to knit when she was four years old, by watching her mother teach Mary, who was then six.
Learning to knit is easier than learning to read (two stitches versus twenty-six letters and thousands of words), and only slightly more difficult than learning to tie your shoes. It takes only the patience, attention-span, and dexterity of an average six-year-old, or that of an especially observant and tenacious four-year-old. It requires minimal equipment, it's extremely portable, and it can be done in the dark or by the blind, and it's very easy to fix mistakes. Frustrating, but simple.
Victorian-era knitters tended to use finer yarns and smaller needles than we use today - there is no evidence that I've found of worsted-weight yarn being used for mittens, or really anything other than rugs, blankets, or heavy shawls. There are patterns still available for mittens knit on the equivalent of US 00000 needles, using silk thread around the same thickness as sewing thread. These are fancy mittens, of course, though they're probably warmer than you would expect - silk is an excellent insulator. For everyday mittens, meant to be worn by children for one or two seasons and then likely unraveled and reknit into larger mittens or something else, a plain wool yarn would be much more practical. The yarn still wouldn't be any heavier than DK at most, though. I've chosen to use a light sportweight yarn - Knit Picks Wool of the Andes Sport. It's inexpensive, 100% wool, not too soft (scratchier yarns tend to be sturdier), but not too coarse, and I will be able to use the leftovers for other projects that I'm planning for the blog. I haven't decided what I'll use for the knit lining, but it will be a fingering weight yarn.
The basic skills required for knitting basic mittens:
Working in the round
Picking up stitches
Weaving in ends
Knitting a second mitten after you're already sick of the first