Sliding is an excellent skill to build on balance, strength and coordination. It can all start by simply using the butt of the hockey stick to propel the chair rather than pushing. As confidence is gained, transfer to the floor and try moving around just using arms and hands. It's usually easier to do this going backwards and dragging the legs along. Be aware of any sores or abrasions when trying this (try placing a slippery blanket underneath). This can progress to using floor level scooters or indoor sledges.
This motion can help with activities like sledge hockey, cross country skiing and others. Scooters games are also great later on because it puts all participants on an equal level making it fun and challenging for everyone.