It kinda sound's like mom and dad might be getting the Dr. to say what's convenient for the kid. However I have seen coaches take it on their selves to work a injured kid hard during practice but not let him play games.
But to answer the question, it's hard to go against the Dr without leaving yourself wide open. If a kid has a bad ankle I like for him to do sit ups, and medicine ball training, while the rest of the team is running!