The "Toxic" singer checked into Promises Residential Treatment Center on Feb. 21 to deal with her substance abuse issues.
And estranged husband Kevin Federline brought the couple's two children--Sean Preston, 17 months, and Jayden James, six months--to visit their mother.
Federline and his sons left his house in Tarzana, California, in a black Lincoln Navigator Sports Utility Vehicle, outfitted with curtains to ensure privacy, for the 6 a.m. rehab visit.
A source tells Us Weekly magazine, "It seems like Britney is struggling being away from Sean P and Jayden because Kevin let her spend four hours with the kids."
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