For Katie's shirt, I used swimsuit material, hoping that it will be a quick dry material and therefore closer to a real running shirt. The material wasn't as stretchy as ribbed cotton, so when I made the collar, it ended up being HUGE. the solution to my problem was to attempt a V neck instead...it kind of failed, because i had no idea what i was doing, but Katie likes it and that's all that matters.
For DJ's shirt, I resized one of Elijah's old T shirts. Yes, highway 69 is a real highway...I haven't ironed this shirt yet, but the little guy was in a hurry to put it in, since his sister already had hers. I was very pleased with this one, in person, you would never guess that it was homemade. :)
Post Script, I have three out of six straps done on my big project, hopefully I can post the results later in the week!