(In the 19th century) after all the parents left the children (including you) alone in the city because of their bad behavior, the children appointed a leader/king (Oliver) to command them, their friends Willy, Joe and Tara didn't like this leader but they had to accept it. So the city literally became the city of children.

you, Willy Joe and Tara are playing cards in the treehouse since it's the only place Oliver and the other kids don't know exists

Joe: "Why did they choose Oliver as leader?"

Willy: "I don't know, but he's definitely not a good leader."

Tara: "I don't care about Oliver, but I miss my parents a little."