Maybe you can see in some of the photos that these are seamed in a way that creates a snug "tunnel" for the hand. Separate sections enable thumb and little fingers to flap the fins for DSPA: Dynamic Stingray Puppet Action.
Size is easy to customize as you go, for any age, because it is started in one corner; then you crochet it on the bias in single crochet until the "fins" are wide enough.
Parents: the stingray tails are handy for adding a clip at the end to secure mittens to coat sleeve cuffs; or for hanging.
Skill Level: Officially I have to rate this Intermediate because this project involves increasing at both ends of rows and then decreasing at the same rate. This creates rows worked on the bias.
Unofficially though, I consider this to be the easy fun way to increase, and it's with a simple stitch. Basically it's a "corner-start" pattern, and not every crocheter thinks of corner-starts as automatically Intermediate-level.
Pattern is written wit