The use of repetition creates a sense of childlike excitement because as children, we have very limited vocabulary and cannot express our excitement in multiple ways. The easiest way is just to repeat what made us excited without explaining it or saying it different.
If the repetition is present in a text, it mimics the language of a child to enhance the sense of childlike excitement by relating to the readers personal experience as a kid and our experiences observing children be happy and excited.
