I put together a whole reindeer games gift set for my friend's little boys last year. More on that soon. Here is the shirt I put together. I googled a bunch of shirts and created some pieces. You can download those for free here. I used the double sided magic sizing. The instructions are on the package. Basically, you cut the same shapes out, pull one paper off the back, press it stick side to the back of the fabric. Iron.
Peel off the other side of the paper and press the sticky side to your shirt. Iron again.
I could only find one of the sizes in brown, so I bought some dye and dyed a white shirt. In the future, I'd probably grab all white and dye them all so there wasn't so much variation, but the kiddos are still working on their alphabet, there are a few years yet before they are critical about the shades of brown in my projects.