The competition has run successfully since the 2008/09 season - and the Land Rover Premiership Rugby Cup is the first national grassroots tournament officiated by Premiership Rugby.
Over 40,000 children have played in the tournament to date, with the winners from each festival taking part in the Parade of Champions at the Aviva Premiership Rugby Final at Twickenham in May, where they are presented to a sell-out crowd at half-time.
Speaking ahead of the event, Thomas said: "These grassroots initiatives - supported by partners such as Land Rover - are the foundations of rugby in the community, and something we should be really proud of.
"I'm sure there will be some of the next generation of Worcester Warriors players on show. I still remember playing at this age and loving my rugby so I can't wait to get along on Sunday and see the children enjoying the game like I did."
Land Rover is proud to be supporting the development of rugby through their sponsorship of the Land Rover Premiership Rugby Cup, Premiership Rugby Academy and the award-winning Hitz programme.