A highly intelligent and mischievous four-year-old who creates much of the story’s action, known for his pranks and confidence. He looks up to his older brother, Peter, and helps drive the plot's conflicts.

Peter's best friend from Manhattan, whose life is shaped by his parents' divorce. He is supportive and emotionally expressive, and his friendship with Peter provides stability.

A hardworking and patient figure in the family, balancing the demands of work and caring for her children. She often deals with exhaustion and Peter’s emotional outbursts with humor.

Emotionally distant, he relocates the family to Princeton to pursue writing but remains disengaged from Peter. His decision catalyzes the family’s move and the changes they experience.

The youngest member of the Hatcher family, she is a joyful presence and helps Peter embrace his role as a big brother. Tootsie's early development coincides with the family’s time in Princeton.

Peter's new friend in Princeton, who helps him adjust by sharing local knowledge and humor. He complements Peter's life without replacing his friendship with Jimmy.

Fudge's first friend in Princeton, known for his precocious and outspoken nature. He plays a significant role in the story's climax with his adventurous, unsupervised antics with Fudge.