Robert "Robbie" Hartlepool is Rosalind's 7-year-old brother from the Jacqueline Wilson book Four Children and It. He is also Smash and Maudie's half-brother, Alice's stepson and David's son. He loves animals, cooking and playing with his plastic zoo. He wishes he can climb trees and that his animals come real.
- Rosalind - Robbie's older sister. She cares for him deeply.
- Smash - Robbie's 10-year-old half-sister. She is usually rude to him and calls him Tree Boy.
- Maudie - Robbie's little half-sister. He sleeps with her at night.
- Alice - Robbie and Rosalind's stepmother.
- David - Robbie and Rosalind's father.
- The Psammead - A furry creature who grants Robbie's wish for him to be good at climbing trees.
- Robert - A boy from Five Children and It.
- Cyril - An older boy from Five Children and It.
- Jane - A girl from Five Children and It.
- Anthea - An older girl from Five Children and It.
- The Lamb - The youngest boy from Five Children and It. He is the same age as Maudie and looks like a boy version of her.