Children love ballons and balls. Why not combine both for maximun fun? Push the straw into the base of the Giant Balloon Ball and then blow into the other end to inflate it. Once inflated to the desired size, remove the straw and the Balloon Ball will stay at that size.
Throw the ball, bounce it around and squish the air-filled balloon and it will retain its size and shape. Reinsert the straw and the air will leave the balloon again, deflating it ready for next time.