I am going to frost my sons cake with store bought frosting. Will fondent still stick or work with the store bought frosting?

Depending on how big of a cake you are doing....

I would think if you are doing an 8 or 10 inch.. you should be fine. The store bought icing is pretty soft from what I remember. You need a somewhat stiff icing to hold up under fondant.

Are you talking about a tub of Wilton buttercream...or a can of Duncan Hines?