Obviously, Tom, you have an accident waiting to happen. The code says you have to have ballusters with no more than a 3 or 4 inch space between them so a kid does not get his head trapped between them and strangle. Check with a stair manufacturer or your local building authorities on the exact distance. That would be a good start. There should be a listing for stair manufacturers in your phone book. I don't know if yours are wood or metal but this is probably a job for the pros.
We had some excellent childproof gates that came from Europe and I don't know if you can get them here but it sounds like you need one top and bottom.
Certainly I hope you get this resolved immediately.