D.W.
There really isn't one that is safe. I have used a cool mist vaporizer. My daughter, youngest, gets really bad, almost croupy. The best thing that has worked for me is the vaporizer. Using cough medicine on them at this age is not a good thing. They really don't recommend it, probably why you don't see much of it. The other thing I do for comfort sometimes at night is a little tylenol or motrin, tends to calm them and believe it or not, has helped her with the coughing too. We have had many bouts of croup and I understand what you must be going through and feeling, but for non-productive coughs, there really isn't anything.