If you're looking to give your future Open champion a perfect start, Penn tennis balls are the number one choice. The best-selling tennis ball in America, Penn is the standard by which all others are measured. An ideal tennis ball for kids with a bit of experience, the QST 60 is the next step up from the 36 beginners' ball. For players around the age of 9-10, the ball features lower compression for controlled bounce and 50% reduced speed. The junior tennis ball is great for young players still mastering the basics of ball control. Everyone has to start somewhere; start your children off with the best.