I used to do this to my girls' jeans after school let out. Great way to boost the summer wardrobe for next to nothing! Transform an old pair of jeans into adorable summer shorts using bias tape. Instructions on the site.
do it yourself divas: DIY: Hem Jeans Fast & Easy - NOTE: she doesn't do an overlock stitch on the hem, after cutting off the excess fabric, which I would recommend. Leave at least excess fabric at the hem to overlock stitch, then iron flat