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• Brian Stepanek as Tom, the father of the Harper family quadruplets. It is a running gag in the series that he cares more about his possessions than his children, but he loves his family and is a kid at heart.
• Allison Munn as Anne, the mother of the Harper family quadruplets who usually gets caught up in Tom's new obsessions.
• Aidan Gallagher as Nicky, the youngest of the Harper quadruplets. He is shown to be quite comedic, quirky, and easily confused. It is shown that he is a talented chef.
• Casey Simpson as Ricky, is the second oldest of the Harper quadruplets. He is the smart one of the group, always seen carrying a book or doing his homework. He is also a neat freak and a bit of a goody two-shoes, though he occasionally tries to prove to Dawn and his brothers that he can bend rules as well.
• Mace Coronel as Dicky, the third oldest and easy-going Harper quadruplet who cares a great deal about his appearance. He always takes the easy way out. He ships himself to Australia in "Quadcodile Dundee".
• Lizzy Greene as Dawn, the oldest of the Harper quadruplets. Although she's always seen bothering her brothers, she does care about them deeply. There is a consistent rivalry for the leader spot of the quads between her and Ricky.
• Gabrielle Elyse as Josie (season 1), a worker at Tom's sporting shop and babysitter for Nicky, Ricky, Dicky and Dawn.
• Kyla-Drew Simmons as Mae (recurring, seasons 1–2; main, seasons 3–4), the quads' friend and Dawn's best friend. She often calls herself "the fifth quad".

Recurring

• Lincoln Melcher as Mack (seasons 1–3)
• Jason Sims-Prewitt as Principal Tarian (seasons 2–3)
• Siena Agudong as Natlee (seasons 2–4)
• Hayden Crawford as Dooley (seasons 3–4)
• Theodore John Barnes as Miles (seasons 3–4)
• Isabella Revel as Avery (seasons 3–4)
• Ariana Molkara as Sadie (season 4)

Ratings

Awards and nominations