My son used to get it every winter when he was little. He was older than your grandson (he was maybe 2 yrs the first time he got it), but he got it every winter at least once until he was around 5. Watch for stridor (that's when their skin pulls across their ribs tightly, or sucks in around their collarbone/throat when breathing). That needs immediate medical intervention, not just steam from the bathroom.
My son would not be able to sleep, and the barky cough upset him so much that he would cry and that just made everything worse. He was scared by how he sounded more than anything else... We live in the deep south, so if he got it before Xmas, we had to use the steam shower method of home treatment, because usually it was not cool enough outside at night. If it was January, then I usually could take him into the guest room in our home where I would open the bedroom window wide to let in lots of cold air, then lie with him on the bed right near the window with the two of us all wrapped up in warm blankets. His whole body doesn't need to be cold, just the air he breathes needs to be cold. And I think the outside cold air (unlike sitting in a very cold air conditioned space) has moisture in it that is helpful, too.
Croup is not just a "bad cold". It is inflammation around the vocal cords and trachea, which can close off the airway. That narrowed airway space is what causes the "bark". When kids are little, they have a narrow space there to begin with... so this is something that kids get less susceptible to as they age. My daughter NEVER had it. But it was every winter with our son.
There is medication that can reduce the swelling to ward off continuing symptoms on subsequent nights.
I was always exhausted when our son had it, because they can't sleep. And you can't either. The BEST thing we did, was the "sleep in the guest room with the window open" routine, when it was cold enough out to be effective. I just closed the door so the rest of the house didn't get all the cold air, and both of us would be able to get a little sleep curled up together. He was comforted by my presence and the snuggling, and I was comforted by being RIGHT THERE totally aware if he woke or slept and could watch for stridor easily.
My son never had the "bark" during the daytime. Only at night. Classic croup.