Peter's precocious 5-year-old brother, known for his curiosity and penchant for creating chaos, who looks up to Peter and finds a new friend in Mitzi.

A sometimes antagonistic peer to Peter vacationing in Maine, who reveals different aspects of her personality, including her ability to take on responsibilities like babysitting.

Peter's lively grandmother who provides understanding and comfort to those around her, and surprises the family with her adventurous spirit.

Peter's best friend, who joins the Hatcher family for part of their Maine vacation, providing support and humor to Peter amid family chaos.

Peter and Fudge's parents, characterized by their differing approaches to parenting, as they manage vacation life and occasional mishaps.

A young girl Peter and Fudge meet in Maine, who becomes Fudge's friend and playmate, bringing excitement and connections to new adventures.

Jimmy's father, an artist whose unexpected response to an accidental incident provides a lesson in adaptability and humor.