Federline is to jet in to look after the couple's two boys, Sean Preston, 4, and Jayden James, 3, while Spears tours and is also planning on raising money for a children's charity. Federline, who has put on weight since he was a back-up dancer for Spears, is also expected to be looking newly slim when he arrives in Australia. A contestant on US reality show Celebrity Fit Club, Federline has already lost 20kg and is expected to be looking even leaner. He and the boys will join Spears for her concert leg in Brisbane.