What makes children to not remember the events and situations from the first three, four years of their life yet they do pick up on, and remember, the things they are taught regarding upbringing?

My earliest recollection of something was from when I was four years old (about), from the years before that I remember nothing.
But supposedly(obviously) it is important to teach children about good and bad and everything else concerning upbringing.
Why do we remember the one latter not the former?