How do you explaint to a 2nd grader how to find 2/3 minus 1/4?

I wouldn't. I doubt if this is part of most 2nd grade curricula.

http://www.google.com/search?q=second+grade+fractions&biw=1920&bih=955&tbm=isch&tbo=u&source=univ&sa=X&ei=C0gTVbCOJ4PEggT8qoCABA&ved=0CB0QsAQ