Child suffers sudden short of hearing in one ear after a cold?

Very common: This is because fluid has likely built up in that middle ear area and it's like trying to hear underwater. First, be patient - these almost always clear on their own. If old enough, have child chew gum, "pop" ears like you do on a plane, eat gummy bears. If pain develops, then need to see doc, otherwise try to wait it out a bit over next couple of weeks and see if hearing returns.