Do you remember these onesies? 
I started by printing off my initial in a font I liked. Then I placed the printed initial under the freezer paper and traced. The freezer paper is a bit translucent so you can easily see to trace your pattern. 
Next, I ironed on the freezer paper to the onesie. Make sure you empty the water reservoir and iron the shiny side of the freezer paper down. Be sure to place a piece of cardboard inside the onesie to prevent bleeding. I used a sponge brush to paint. I did two coats to get into the ribbing. 
Once the paint dries, remove the freezer paper and you have a custom monogrammed shirt!
The shirt I made for my son last year really held up to washings. I turned it inside out and washed it in cold. When picking out a shirt or onesie for this project, be sure to get one with fine ribbing. When the shirt stretches, it can distort the image some. I think these would be fun to do for kid pictures or a birthday child! Really, you could do so many different patterns/designs!
