There's a surprise - Susan's a geek who likes Doctor Who! (I did have a Dalek shirt, but it said it was "XL" and my tiny mom couldn't fit into it, which just shows you that you should try on the shirt before you stencil on it!!!)
With a few pieces of fabric and some fabric paint from the store, you can make some really lovely designs. They can try painting freehand or with stencils. I like to use small pieces of fabric the kids can sew into something else (we're doing sunglass cases next week, so if you want to follow along, you'll want a piece of fabric 8 inches wide by 7 inches high for the outside.)
Fabric stencilling instructions (part 1) - The basics for fabric stencilling.
Fabric stencilling instructions (part 2) - If you want to get more complicated!
Fabric stencilling templates - These are actually wingding fonts blown up large. This is a great way to get pictures suitable for stencilling.
You can stencil on any cotton fabric you can find. Just make sure you heat set it before you wash it!!!
Have fun. Once you start stencilling, you will find it hard not to decorate everything you own!
Oh, and here's a cute stencilling idea for putting your name on your camping chair!