Croup is only about as contagious as the common cold, so whatever precautions you practice when someone in the house has a cold, should work. Typically, if his cough is worse at night, steam up the bathroom and let him sit in there and breathe in the moisture for a while. Of course a humidifier in his bedroom works wonders too. Usually with croup, the younger the child, the worse it is. My oldest spent 2 nights in an oxygen tent in the hospital when he was less than a year old. It can be pretty scary.