I bought these iron-on letters at Wal-Mart ($0.47 a piece) along with some sports fabric. I probably could have found something cuter, but didn't feel like going anywhere else, so this did the trick just fine.
This is the same process I used on my patches for Hallie's jeans with the Wonder Under.
I first printed off an 8 that I liked and cut it out.
Then I used that as my template for my iron-on. I just traced around the template with a sharpie onto my fabric that I had Wonder Undered up.
Then I cut that out, ripped off the paper backing, and ironed it onto his shirt along with the letters to make his name. But inside the shirt I ironed on some of this stabilizer to make it easier when I zig zaged the edge of the eight. I'd recommend this step, it makes for much smoother results.
Once you have your number ironed on and your stabilizer in place head to your sewing machine to outline the whole thing with a zig zag stitch. You don't have to do this step, (and then this would be a no sew project) but I like the look of the stitching, and think it will help the shirt to last longer.
And there you have it, one eight-year-old-birthday-boy-shirt for one eight-year-old-birthday-boy.
I thought that the front looked a little plain with the back all jerseyed up, so I added this small soccer ball that I had cut out from the fabric.
He liked it. That's all that matters to me, Happy (early) Birthday Dallas!