WHILE Kevin Federline partied in Miami Beach this weekend, Britney Spears stayed at home...with the kids E News can confirm that Britney had a 12-hour overnight visit with her two sons Saturday night at her Los Angelesn+1/2home. "The kids were picked up before noon on Sunday," says a source. It was Britney's first overnight visit since Spears lost visitation with her kids following her infamous visit to the UCLA psych ward in January. Commissioner Scott Gordon, after being presented evidence that Britney's mental health has improved, modified the terms of her visitation last week to allow overnight visits. Meanwhile, K-Fed picked up where he left off in Las Vegas two weeks ago and partied at Miami nightclub Mansion on Friday night. Federline, who's reportedly working on a new song tentatively titled, "Daddy's Home," was scheduled to return home to LA on Sunday.  " E