You should not be worried when your son falls accidentally just because he had the MRSA infections earlier. The infections might have already been eradicated when he received the first treatment. To get these infections again he will have to have physical contact with a person with the same. However, you can seek assistance from a doctor to get informed on how you can keep him from getting any other bacteria infections.
There is no cure for MRSA. Once you have it, you have it. You can have repeated outbreaks or you may have one over your life. A cut or a scrape should not be too much of a concern, but if you are going into surgery, this is something that needs to be disclosed to the doctors and surgeons.