These are Cat Mittens by Jorid Linvik, available as a Ravelry download. She also has patterns with fish, dogs, frogs, and birds.
I'm using Claudia Hand Painted fingering weight in Chocolate and Magic Elixir. The one on the left was knit on US 1.5 needles, and is too small. I've switched to size US 2, and I think they will fit fine but may be a little shorter than I'd prefer.