These ingenious little sleeves look very sophisticated when done, but nothing could be easier to do. They were inspired by the Vogue children's dress pattern shown below:

Here are the instructions for creating these easy little sleeves. Basically, you will cut two squares, approximately 12", on the bias. Then slit the squares as shown. Hem outer edges and slit, leaving 2" of slit unhemmed (shown in red). Open the square up at the slit and attach to armhole of dress as shown, matching center of slit with shoulder seam of dress: