Epistemology and the aprior

Immanuel Kant had a slogan that encompassed his work about knowledge and internal philosophies of mankind: “Thoughts without content are empty, institutions with out concepts are blind.” Kant’s epistemology philosophy was revolutionary with the discovery of the “aprior,” which means to exist before experience. This idea was the basis for Kant’s argument on innate idea at birth. He believed that every person has these concepts like geometry and arithmetic when they are born. This doesn’t mean they have the knowledge to communicate, but the knowledge is there. These ideas were controversial in the philosophical community. The aprior was very similar to Descartes idea that we are born with innate ideas, but Kant said that these ideas are not derived from a greater being like Descartes and Plato thought. These concepts with in the human mind “…are derived from certain fundamental categories which are presupposed by experience.”(Kant)
These ideas make sense to an extent, but I have a problem with the foundation and fundamental existence of the aprior. The ideas need to be formed by an individuals experience and cannot be pre-existing. I would agree that these ideas are know by man pre-existing the birth of a child, but that doesn’t mean the newborn will be able to understand the concepts in the future. Kant basically says from my understanding that everyone starts with the prior knowledge. This is wrong because knowledge comes from the experience and there are no preexisting thoughts about experience upon birth. Kant’s ideas revolving around knowledge from experience are strong, but the creation of these controversial ideas can not supported by empirical evidence.