I was an extremely happy child until around age 7

My parents have often told me that I was by far the happiest of all their children until I was around 7. I remember it that way too. Im kind of confused as to what could have caused such a shift in my happiness. There werent really any mayor unfortunate life events that I can link to this. Can any of you relate, and do any of you have a clue as to what could have caused me to slowly start becoming a sadder child? Thanks