02/23/2008 at 03:20 PM EST
was reunited with her sons for three hours on Saturday.
After lawyers for Spears and Kevin Federline
reached a visitation agreement Friday
, the pop star saw her children Preston, 2, and Jayden, 1, for the first time since Jan. 3
The boys left Federline's Tarzana house Saturday morning – put in their car seats by their father, according to photographers – and were driven by Federline's bodyguard to Spears's Studio City home.
A source involved in the case says, "The real hero was [Spears's father] Jamie. He has taken charge, and she has visitation again."
Sources confirm to PEOPLE that Jamie and Britney's psychiatrist were present for the visit.
After a three-hour stay, Spears's sons left again in the back of Federline's grey Dodge truck driven by his bodyguard.
Reporting by PERNILLA CEDENHEIM