Mckenna Grace and Iain Armitage have joined 'Scoob'.

The 10-year-old actress - who is best known for her role in Netflix's horror series 'The Haunting of Hill House' - and 10-year-old Iain, who rose to fame playing Sheldon in 'The Big Bang Theory' spin-off show 'Young Sheldon', will voice young Daphne and Shaggy, respectively in the new Warner Bros. animated Scooby-Doo movie based on the iconic children's cartoon.

The latest additions to the cast come after Mark Wahlberg and Jason Isaacs were announced as superhero Blue Falcon and villain Dick Dastardly as well as 'Hangover' actor Ken Jeong and Kiersey Clemons who were confirmed to portray Dynomutt, Dog Wonder, a pooch with mechanical robot parts, and Dee Dee Sykes, who was one of the smartest members of Captain Caveman's Teen Angels group.

Frank Welker will voice the titular pooch, after voicing crime-solving Mystery Inc. gang character Fred Jones since the animated comedy TV series 'Scooby-Doo, Where Are You!' made its debut in 1969.

Instead, Zac Efron will voice Fred for the forthcoming film and Amanda Seyfried will be Daphne Blake, while Will Forte will play Shaggy Rogers.

The Mystery Inc. gang - who aim to solve crimes alongside their canine companion Scooby - will be completed by Gina Rodriguez as Velma Dinkley.

The movie is set to be released in May 2020 and will be the first time Scooby has hit the big screen since 2004's 'Scooby-Doo 2: Monsters Unleashed', which followed on from 2002's 'Scooby-Doo'.

Neil Fanning voiced the canine in both movies, while Freddie Prinze Jr. took on the role of Fred, Sarah Michelle Gellar played Daphne, Linda Cardellini was Velma, and Matthew Lillard voiced Shaggy.