@Almita - I do a lot of brick making myself and there are two ways you can minimize cracking. Try adding metal supports to the bricks horizontally -- it keeps them together better and if a crack does form, the metal supports keep it from getting too big. Using chicken wire in the bottom of the bricks is also a great idea.
It sounds to me like your problem is actually that the bricks are getting too hot. If they are in direct sunlight, the water in the cement dries out too fast -- causing cracks. Try covering your bricks with plastic. Avoid using paper, it will dry them even faster.
Hope this helps.