By using a low-energy tennis ball that compresses on impact restricts the velocity and distance. These balls let players enjoy the same experience they would have on a full-sized tennis court with a high-compression ball. Low-energy tennis balls are used by USTA professionals to teach tennis to young children. You can use regulation tennis racquets on our Multi-Courts but our customers find the game more enjoyable with 21″ – 24″ junior tennis racquets. Two 21″ racquets are provided in the WanheSport Fun Gear Pack along with low compression tennis balls.