I just made my first t-shirt quilt last week. I used a light weight fusible interfacing first. Then cut the shirts to size. Then I just used the shirts like a normal piece of fabric, but use your walking foot! If the shirts are small, just adjust the size to fit the shirts. For your project, your local quilt store will be happy to help with that, I'm sure. Mine used small adult t-shirts, so I got some sleeve edges in it. I used the BQ3 pattern because I wanted a more modern look. Here's my link if you want to see it.
http://www.quiltingboard.com/t-126291-1.htm