I really wish I could take credit for this idea. I found it on the net. I did tweek it just a tad.
Find a ladies t-shirt. I think this one was a medium. It was her mommies. Sew from the neck down the shoulder seam all the way to the bottom of the sleeve with elastic thread in the bobbin. Make several passes back and forth. Do both sleeves this way. Find about where the waist would be on a small child. I guessed since small child had went home. You want to go just a tad below the waist so it can blouse up. Sew a couple of round around the middle. The picture I saw I didn't like the way the sleeve was to big. I fixed this by making two passes around the sleeve on the hem. We tried it on and decided the neck was to big so I sewed around the neck a couple of passes. Next time I think I will just sew a section in front and in the back, not a circle.
This took maybe 20 minutes from start to finish including several oops as I sewed where I shouldn't.