DD is 8 and been croup free for 2yrs.
I think there is no way to really avoid croup, as its viral, but I second icy poles etc, for croup at least, don't know if it would be any good for asthma though.
during really bad nights I'd wrap dd in a blanket and walk around the back yard for a bit, or if we had to go to ED during the night, the cold air would always calm it down a little.
Hospitals are definitely saying no steamy bathrooms for croup.
A few of the nurses recommended echinacea tea, pita to find, most health shops have it though, I'm not really sure if it helped :/ but maybe it works for others.