This weekend at my son's baseball games I watched a group of younger siblings entertain themselves with old rackets and an old tennis ball and some baseball gloves. They all got together and invented a game using the equipment they had and the space available to them. They agreed on the rules, divided into teams and played for HOURS! Any arguments were decided by the group, and even the youngest was included.
Kids don't need the best equipment, instruction or even space. They just need their imaginations and some time. It was a joy to watch.