So, taking his suggestions, I measured him in his favorite jacket, since this is the size he wanted.
He took me by the hand and led me directly to where he KNEW the yarn was already in my house-smart kid, he pays attention!
But then he asked for thumbholes to be added to the cuffs. No problem, just make 'em like wristwarmers! I tried it on just before I went back to Michigan before I joined the sleeves to the body and realized it was a perfect fit for right then. No room for growth. Since I wasn't going to get it done prior to boarding the plane, we decided to add a little extra length in the body and the sleeves.
Then I finished it right after I got to Michigan so I had mailed it to him. I had THOUGHT I'd have left on Valentine's Day, February 14th. Since I didn't leave until the end of March, I had to wait until yesterday when his schedule met up with mine to get pictures of him wearing it so I could see how it fit.
I do believe we got him some growing room. Child sized 12 with extra length in the sleeves and body, just under 3 skeins of 'I Love this Yarn!' in Navy. Then add in one older brother to stand behind my shoulders to make him laugh while taking pictures to show his new big teeth! wa-la...makes the knitter happy!