Fill in the center of the circle with a black marker for the pupil, leaving a small white circle in the center as a highlight. Repeat for the remaining Ping Pong balls.
Tip: The number of Ping Pong balls you need will depend on how big the shirt is and how full you want it to be. Dollar stores frequently have table tennis balls. They often are not the best quality for the game, but they are great for crafting.
Lay a t-shirt on a flat surface and insert parchment paper between the front and back layers of the t-shirt covering any space where you will be attaching eyeballs. With a hot-glue gun, place a dab of hot glue on a Ping Pong ball and press in place on the t-shirt.