These are kids' tennis balls used in PLAY&STAY. They are larger than standard balls and have lower air pressure, making them ideal for children who are new to tennis. How about these for kindergarteners and lower elementary school students who are just starting to play tennis? The air pressure is originally low, but it is likely to be even lower than a new ball. There is also some fuzz and dirt. I think they can still be used for ball feeding practice or practice with a low net. Please judge the condition from the photos. *Please consider these as recycled items. Manufacturer: Yonex (39 balls) and Dunlop (1 ball)