Kevin Federline's lawyer Mark Vincent Kaplan filed the order at the Los Angeles
Superior Court on Wednesday.
The 28-year-old is hoping he can show cause for being awarded primary
physical custody following Britney's recent erratic behavior.
A source told People magazine: "Kevin is worried Britney is exposing the
boys to unnecessary risk. His lawyer hopes to get Kevin primary custody."
Kevin and Britney, whose divorce was finalized less than two weeks ago,
originally agreed to equally share custody of 22-month-old Sean Preston and
10-month-old Jayden James.
However, Kevin was reportedly reluctant to sign the divorce settlement
papers over growing concerns for the 'Toxic' singer.
Britney, who entered Malibu's Promises rehab center earlier this year, has
been a regular fixture on the party scene.