The only thing I modified about her tutorial is that I sewed through the layers with a needle and doubled up thread before I snipped the outside edge. I didn't want little t-shirt shreds around my house- t-shirt pom poms scattered everywhere were going to be enough trauma. ;)
In this picture you can see the ends of the white thread I used to hold the pieces together. I wasn't precise about my stitching line, and I'm sure I missed a few strands, but at least this way the whole pom pom wouldn't explode. When I tightened the inside t-shirt tie, I also tied off the strings tightly, to secure the strands even more.
I was going to try to take a picture of the children chucking these at each other, but how 'bout you go make some and hand them over to your kids- just see for yourself what happens. :)