Sebastian Croft as Archibald Arnold

Charithra Chandran as Amelia Brown

Tanner Buchanan as Billy Walsh

Kunal Nayyar as Rupert Brown

Nick Frost as William

Guz Khan as Mr. Atkins

Lucy Punch as Lilly Arnold

Tim Downie as George Arnold

Daisy Jelley as Amber McKenna

Charles Camrose as Tony

Maisie Peters as Maisie Peters

Paxina Tuvuka as Talissa

Dhanushka Anson as Jules Brown

Nael Ameen as Yousif

Madeline Holliday as Penny

John Richmond as Quigley

Russell Streiner as Johnny (archive footage)

Judith O'Dea as Barbra (archive footage)

Bella Induruwana as 5 Years Old Amelia

Henry Reinhart as 5 Years Old Archie

Shaneli Gedara as 9 Years Old Amelia

Casper Knopf as 9 Years Old Archie

Aliyah Soyinka as Student #1

Curtis Antonio Powell as Student #2(as Curtis Powell)

Luyanda Unati Lewis-Nyawo as Maggie

Jocelyn Jee Esien as Ms. Frances

Jett Dyason as Trent

Ben Greenhough as Soho Waiter

Joyce Branagh as Joyce Branagh

Esther Agbakwuru as Nurse(uncredited)

William Cherry as Student(uncredited)

Nathan Hall as George (Student with Fedora)(uncredited)

Samuel Hayes as Cinema Attendee(uncredited)

George Imerlishvili as Student(uncredited)

Killian Kilduff as Hot Dog Seller(uncredited)

JJ Martin as Student(uncredited)

Freya Pearson as Student(uncredited)

Edith Slow-Noble as Teenager(uncredited)

Jack Smith as Swim Team(uncredited)