Glad you are top of this. It is indeed a problelm and another "code" issue......they just keep coming up. What I was trying to picture was whether or not you stair is cut into the interior of the floor space? If this is the case, do you have railings around the stair, thus having another way for the little "pumpkin" to crawl "over" the top of your railing, and cracking his skull?
If this is the case, we need to consider some sort of temporary wall "around" the stair opening. You could do this easily with a temporary stud wall, up four feet or so, that you could dismantle when you feel safe with the situation or when "pumpkin" goes to college, which ever comes first. Of course, depending on your plans for additional children, you may wish to make the solution a permenant one.