Sub-category post displayed category archive

Hello house, I want somebody to help me out of this problem, the problem is that subcategory post display on my site whenever a category is clicked. What I am trying to say is that i have parent category A with post in it, and it has some subcategories with post in them. If a visitor should click on category A, instead to display its post, it will display the post in subcategory and this is misleading. Is there anybody with ideal of what I can do to correct this? Some of the prescribe solution I saw online did not work for me, may be because I use twenty ten theme. My website is