Federline took Sean Preston, 17 months, and Jayden, 5 months, to the facility during the weekend, People magazine said.
"The kids are his No. 1 priority and they always have been," a source told People. "He only wants the best for Britney and the kids."
Saturday's visit was the second time Federline has visited his estranged wife. He also went to the center Friday without the children.
Spears, 25, checked into the residential facility last Tuesday but left the next morning. She returned Thursday night.