The split between three-time Wimbledon champ Boris Becker, 33, and his estranged wife, Barbara Becker, 34, appears to be growing nastier. Newspapers in Becker's native Germany reported yesterday that the athlete filed for custody of the couple's two children (Noah, 6, and Gabriel, 1) in a Munich courtroom. His attorneys contend that Barbara Becker uprooted the children by taking them to the Beckers' Miami home. Barbara Becker has filed for alimony and child support in a Florida courtroom. No divorce papers have been filed.