Pixieval, I saw a tutorial once for making baby pants out of t-shirts. So, I tried that and then eventually made some shorts and then tried making leggings. To make the pattern I just used a pair of leggings that fit her, folded them in half, laid them out on paper and traced the right side, flipped them to the left and then traced that side, making one pattern piece ...does that make sense? Oh, and of, course, I added seam allowances to the pattern. Then you lay the hem of the pattern against the hem of the shirt...baddabang baddaboom...easy leggings. I love going to the thrift store here in town when they have women's shirts for 50 cents and finding stripey shirts for this purpose.
If you have anymore questions, shoot!