Mallinder said: "With two senior England teams on tour at the same time we are fortunate to have kept such talented players for this tournament.
"Dorian and I were very pleased with the way the team developed throughout the Six Nations and we're really looking forward to competing at a world level.
"The players know that to compete against world champions South Africa and the rest of the southern hemisphere sides they need to take another step up but we have every confidence in them.
"The squad includes Danny Care, Ian Grieve and Tom Mercey who all played in the England U19 team that won bronze at the U19 World Championships earlier this year. Playing alongside the more experienced players who were a part of this tournament from last season will be great development for them."
ENGLAND Under-21 IRB World Championship Squad: Forwards: Richard Blaze - Worcester Warriors, Neil Briggs - Sale Sharks, Chris Brooker - Bath Rugby, Ian Grieve - Bristol Rugby, Jordan Crane - Leeds Tykes, Tom Croft - Leicester Tigers, James Haskell - London Wasps, Michael Hills - Sale Sharks, Mark Lambert - NEC Harlequins, Tom Mercey - Saracens, Chris Robshaw - NEC Harlequins, Alex Rogers - NEC Harlequins, Tom Ryder - Saracens, David Wilson - Newcastle Falcons. Backs: Anthony Allen - Gloucester, Mike Brown - NEC Harlequins, Danny Care - Leeds Tykes, Matt Cornwell - Leicester Tigers, Ryan Davies - Bath Rugby, Paul Diggin - Northampton Saints, Toby Flood - Newcastle Falcons, Ben Foden - Sale Sharks, Ryan Lamb - Gloucester, Uche Oduoza - Worcester Warriors, Topsy Ojo - London Irish, Matt Riley - Sale Sharks