People frequently use precursors in order to obtain your attention. It gets more sophisticated as people grow up but children find it effective early on. One of the reasons they are so enamored with it is parents tend to use that phrase with their children quite a bit to make sure they’ve got their attention and the kids just pick it up. So it’s kind of like a baby talk left over

Adult versions are things like 'You’ll never guess what just happened to me" Or “You’re never going to believe this”