I love a contrasting border on the sleeves of baseball-style tees. I think it gives it a comfy, child-like look. They are relatively easy to do, but they require measuring and pinning, two things I prefer to avoid, if possible. Here's an easier way that turns out just as cute.
First, cut about an inch off the sleaves of an adult shirt (aha! I always find a way to use recycled SOMETHING!).You'll have 2 long strips...Place one strip on your sleeves BEFORE the sleeve is sewn together- when it is still opened flat. Make sure good sides are together, and sew using a 1/4 inch seam.Flip the cuff over, so the good side is up. If you want, iron the seam down towards the sleeve. Next, topstitch on the sleeve right next to the cuff to hold the flap of the seam down and make it look a little neater..Now you can sew your sleeve closed.You can see that this way is not as neat as the measuing/pinning method, however, it works great for kids clothes, and they aren't picky. This little dress uses soft knit material, so I don't have to worry about the seam rubbing the little gal's arm.