The Problem with Cleo

 Hello, I would like to introduce The Problem with Cleo in the Literacy Land series. 

Cleo, a younger sister of Donut always wants to play with Donut and his friends. They also enjoy playing with Cleo, but sometimes they want to play with only themselves. So it was a problem for them that Cleo always follows them. Cleo wants to join the older group and play together, but they don't think so. Cleo comes into their secret room without their permission, so they decide to climb up the tree as their new secret room to see Cleo coming. After that, Cleo comes there and she tries to climb it like them. However, she slipped on a trash can and fells to the ground. Cleo's mother comes and calls an ambulance. While Cleo, her mother, and Donut go to the hospital, the others are afraid her mother will find out that it's their fault. 

What will do Cleo to join their group after that?