I was going to say exactly what momofnerds said, it could be fluid in the ears or an ear infection if his chest has never cleared up. He could have damage in his lungs or a chronic infection there too. Our balance is controlled in the inner ear so I would ask the parents if their doctor has mentioned or checked any of those things. Don't say "I think........" but rather say "Have you thought about........" and it will come across to them in an easier way, not that you are lecturing them, you know?