Maybe it’s expression and imagination.
Children like to name themselves because of their expressiveness and rich imagination. Children who imagine that they are supermen will give themselves a name, and imagine that they are scientists and give themselves a name, so children will like to name themselves.
Children refers to children; infants. Song Qianyi's "New Book of the South" 5: "(Chen Qiao failed in several attempts, and won the first place in his later years.) When he was newly married, he was nearly eighty years old, on the eve of the wedding... It became a chapter of its own, and at the end it said: 'Peng Zu Shang Wen Nian' "Eight hundred, Chen Lang is still a child." "The Comments on the Book of the Former Han Dynasty" Volume 2: "Nv Lu walked to the back garden and saw a child playing."