Scott's making them kiss in this photo:
If you need to try it yourself, here's what I used:
washable felt (the kind you buy by the yard in the fabric section, not the kind you buy by the sheet-of-paper size in the craft section)
coordinating embroidery thread
fabric glue (permanent)
I recommend doing as much of your stitching detail as possible before gluing or make sure you leave the very edges un-glued because otherwise you'll have a heck of a time getting your needle through all those layers of felt, denim and dried glue.
I started each time by gluing a big black square of felt to the inside of the pant leg, generously covering the ripped area. then I just cut my tooth, eye and tongue shapes and glued them in place, added my stitching (for looks only but doesn't hurt that it also keeps things in place) and I was done! My kids were SO excited about these and Bekah's teacher told her that she was going to rip a pair of her own jeans, then send them home with Bekah for me to do this to them! They were the envy of school that day from the sounds of it. I'm working on a couple other pairs too so I'll have to post those next.