Mouse Noses on Toast by Daren King won the Nestle Smarties Book Prize (ages 6–8 years) in 2006, after which King and Roberts collaborated on other titles including Peter the Penguin Pioneer, Sensible Hare and the Case of Carrots and The Frightfully Friendly Ghosties series.
Others include Iggy Peck, Architect by Andrea Beaty, Dear Tabby by Carolyn Crimi, Mrs Crump's Cat by Linda Smith, Hopping Mad by Michael Catchpool, Don't Say That Willy Nilly by Anna Powell and The Dunderheads by Paul Fleischman which was shortlisted for the Kate Greenaway Medal in 2010.
Since then he has worked with Alan MacDonald to create a series for older readers with titles such as Burp, Fetch, Kiss and Pants.
His sister Lynn Roberts is also a writer and the siblings have collaborated on several retellings of fairy stories, including Rapunzel: A Groovy Fairy Tale, which was shortlisted for a Blue Peter Book Award, and Little Red: A Fizzingly Good Yarn, which was shortlisted for the Kate Greenaway Medal.
Roberts has also illustrated the series Wings & Co: The Fairy Detective Agency by Sally Gardner (Operation Bunny: the fairy detective agency's first case, Three Pickled Herrings and The Vanishing of Billy Buckle as of 2013) and the covers for a reprint of Enid Blyton's St Clare's books.