My son is a center, but his coach keeps making him play wing and defense sometimes. Should I be concerned?
Absolutely not! In fact you should be thanking the coach for allowing your son to play other positions. By learning to play all the positions on the ice, your son is learning more than he would than by just playing center. As players get older, hockey sense becomes more and more important and you limit your learning by just playing one position when you are young. Some coaches and parents forget that when your team has the puck, everyone on the team is on offense. And when you don't have the puck, everyone is on defense. At the younger ages, we like to say "no positions, all positions." Kids learn to play all facets of the game and many different situations when they are exposed to every position as a young player.
You would be shocked to find out how many NHL players started their careers as centers but wound up playing wing at some point. After all, NHL teams can only play four centers every night. Versatility is a key to extending your career as you get older. A great example of this is Dustin Byfuglien, who has played both forward and defense in the NHL in the last few years.