I agree that kids have the cognitive ability to read very early.  But the eye-hand-brain connection doesn't develop at the same rate for all.  Your own experience must tell you that.  First they must acquire the tools for reading letters and numbers, to associate the sounds they hear with the shapes they see.   Having the tools helps each student begin to learn on his/her own.
Head start teachers use fun, innovative ways to help that development along.  Yes, parents can foster that process, but some don't know where to begin, and are very grateful for directions.