The sound of feet slapping on the padded ground and little voices twisted by constant motion fill Xtreme Play. Jeff and Julie Austin, owners of the play center, have five children, so they are familiar with the busy chorus. The duo and its staff are also well prepared to keep an eye on youngsters as they bounce from inflatable obstacles or squeal down slides. At a miniature arcade, small hands grab Wii and PlayStation controllers, simulating adventures through castles and the civil-service tests to become a castle inspector. The babble of special events drifts from private party rooms, where pizzas fuel fetes.