I used an old t-shirt of Vinny's (size 12-18 months) that I think I bought at Target when they had a lot of cute licensed tee's. I was bummed when he outgrew it, but I set it aside knowing I would find a use for the shirt. I cut out the image and straight stitched it to the jacket lining back panel before construction. Oh, and that lining....It's my Moby Wrap! It's a heavy weight knit (interlock?) with enough stretch to be cozy and enough stability that it sewed up pretty much like a woven.
I used the faux piping technique like I have in the past and it turned out great. I just wish I had ordered a reversible zip online because the jacket looks so cute both ways. Of course I don't know how it looks on because I don't feel like going to the park today!