From Holiday Knits:

This is an ambidextrous pattern, that is, each mitten can fit on either hand. This is especially useful for kids’ mittens that can get lost rather quickly. So, just give three mittens instead of two and the set will last a good bit longer. If you want to jazz them up a little, do some surface crochet on the back of the and - capital letters R and L are great for little ones just learning their right from left, initials are great if there are multiple sets per family, or just add a little flower or other motif.