If you type in a search for "little dresses for Africa" the site will come up. there are a couple sites that give you instructions or One of the pattern companies (simplicity I believe) has a pattern.
You can also search Pillow Case Dresses. They originally were made out of pillow cases.
We had a work day at a local quilt shop and got 76 dresses in various stages of completion and 45 boy's shorts. I talked to the organizer of the Little Dresses and she said they get very few shorts.
It took me about 30 min to make the first dress and about the same time for the shorts. The dresses are all made the same way. the size is determined by the length so fabric as little as 18"xwidth of fabric works.