Despite Britney Spears's release from rehab yesterday, baby daddy Kevin Federline has no plans to hand over physical custody of Sean Preston and Jayden James just yet. "They are not going to return custody to Britney as a reward for doing her stint in rehab," says a source close to Federline. "Kevin's had the children for six weeks and he will continue to have full custody. Britney has to really demonstrate she can retain sobriety. She was just introduced into a sober lifestyle." The insider adds that Federline and his lawyer are "ecstatic, but cautiously focused on Britney's continuing rehab recovery."