Do we need a multi entry Visa and do we qualify for a multi entry Visa

My son and I are traveliing from Australia to Paris and back via Guangzhou. We would like to stop over in Guangzhou for a few days in both directions and on our return visit we would like to visit Hong Kong by train for a few days and return back to Guangzhou to catch the flight back to Australia. My passport has an expired Chinese visa. However, my son (22 years) has never been to China. Do we need a multi entry visa and will my son qualify for a multi entry visa?