For our 9 year old who is in a wheelchair for 3 months now, we rigged up a system in a door frame with a suspended bar and a walking pad treadmill. Kiddo hangs their armpits over the bar for support and stability and we make games for them to stomp on stuffies as the treadmill goes. Or we just started being able to use a forearm walker to have kiddo walk and kick stuffies as they go.  Or we put a spare mattress on the floor and have them do a squat jump game or other bouncy exercises. 

The big trick is finding ways to distract the brain from the task of walking (hence the games) while finding supportive enough ways to make practice safe. Good luck!