The papers filed in Los Angeles Superior Court and posted on the Web site TMZ.com show Spears is seeking legal and physical custody of their children, 1-year-old Sean Preston and 2-month-old Jayden James.
Spears is not seeking any spousal support from Federline, an aspiring rapper, and asks that they each pay their own attorneys. She has obtained the services of Laura Wasser, who represented Nick Lachey, Kiefer Sutherland and Angelina Jolie, among others, TMZ.com said.
Federline won't be leaving with overflowing pockets since he signed an "iron-clad" prenuptial agreement before the couple wed in October 2004, a source told TMZ.com.
Spears says the couple separated Monday -- the day the newly svelt singer made a surprise appearance on CBS' "Late Night With David Letterman."
Insiders said "a string of events" led to the couple's split.