Answer:
Well don't push them around for 'fun' this could put you and the personal in the wheelchair user in risk of getting hurt. Unless they ask for assistance or help with their wheelchair do not mess with the settings or lock out on it. Don't kick/throw any ball towards the wheelchair, it's very rude and also could hurt the user or mess up and break something on the wheel chair and depending on age and weight could tip them over or startle the person. Don't force the user to feel bad about their use of a wheelchair instead acknowledge the person and find other ways you can hangout and just talk and chill at the playground with them.