Considering the six most important questions in the study of children's learning: One of the questions is: How do changes in the brain contribute to cognitive development?
I am going to assume that because you have selected one of the six questions that you wish to have that one question discussed. Changes in the brain allow connections to be made that contribute to a child's developing understanding of the world around them. For example, a very young baby has no grasp of the idea that an object is permanent; for them, if they cannot see it, the object no longer exists. As the brain gets more sophisticated in its connections to objects, the child can move on to the idea of object permanence even if the child no longer can see it. Thus the child can move forward to ever more complex thinking as the brain continues the process of development.
I'm really not sure if this is what you are looking for, or if you did intend to discuss all six of the important questions. I would be a bit more clear in the way you ask your question the next time.