Sean Preston and Jayden James Federline made a trip to visit their mom in rehab last night with their dad Kevin. "The kids are his number one priority and they always have been," a source says. "He's so stressed out right now. He only wants the best for Britney and the kids." Yesterday's visit to Promises was Federline's second since estranged wife Britney checked herself in for the second time on Thursday night. In other Spears news, her first husband Kevin Alexander is milking some press out of his brief marriage to the popstar by claiming the pair went on drug binges together. "We used ecstacy at night to party and cocaine during the day to stay awake. Then we would take downers like Valium to come down and rest. Britney stayed up three days straight over New Year. I couldn't keep up... She definitely had a problem with drugs when we were together - and that was three years ago... It freaked me out when I saw she had shaved off her hair - that was clearly a cry for help. The pictures have become increasingly disturbing. I have never said anything about Britney and drugs before but I am very, very concerned about her. I am really worried that she will wind up like Anna Nicole Smith and be found dead."