I can totally relate to what you're going through since there was a time I went through these Math problems with my daughter as well. But somehow we've managed to find our way through it and now it's pretty set up with very few hurdles coming our way.
As a beginning, try using some objects of everyday use to teach your son the basics - things like pennies, cookies, buttons, books, cans, or even people - by personal experience I can tell you that this does work more often than not, since kids don't relate such objects with maths problems. It worked with my daughter. Once she could actually see/hold/touch these and perceive them as actual physical objects, she could relate to the problems better and it helped a lot in making her master the basics of addition, subtraction and even elementary multiplication.
To supplement this (and other methods which you may already be using), I would suggest putting into use some of these activities and worksheets (I used them myself and still do at times) -
http://www.mathblaster.com/parents/math ... activities - they are designed specially for second grade students (same as my daughter and your son) and have an interesting mix of things to do. Might help.