HERE. From Dana's Ruched leggings. I thought they would make cute shorts. I pretty much followed her instructions. If you've never seen her site, it's worth a look!
I bought a "new" T-shirt from a local thrift store for 2 dollars and just laid my pattern on top of the shirt, using the hem on the bottom of the shirt so I wouldn't have to hem it myself. DANA'S website has awesome instructions on how to create your own pattern using an existing pair of your child's pants or shorts. Or you could chop off a pair of knit leggings that no longer fits your little girl or using an existing pair of knit shorts.
When the shorts are all finished you just sew 2 lines of elastic thread (About $1.50 at fabric stores) to the outside seam of each leg. It's the black thread in the picture. I sewed one line on either side of the side seam. Or you could stretch and sew a piece of thin elastic. Then sew buttons to the outside and that's it. I think it took me an hour to make these and Lilly loves them.