Peg is The main character, together with Cat. She is a young girl who wears a red hat and blue dress. She explains the situation in each episode directly to the "camera", announces when they have "a big problem", and reasons out solutions to math-related problems. During songs, she pulls out a ukelele and plays it. She has a special blue marble hidden under her hat. Her favorite crayon is "little bluey". She is voiced by Hayley Faith Negrin.
When Peg and Cat get lost riding dinosaurs through a prehistoric forest, they use a diagram to find their way to safety before the Baby T-Rex catches up to them.