Sean Penn has reportedly filed papers to adopt his girlfriend Charlize Theron's 3-year-old son Jackson.
A source revealed to People, "Charlize and Sean are very serious. Charlize says this is it. Jackson already calls Sean daddy. This is the first step toward them getting married."
US Weekly also quote a source as saying, "Sean always knew that to truly earn a place in Charlize's heart, connecting with Jackson was one of the most important parts."
Theron adopted Jackson in 2012 when he was 4 months old. Penn has two children with his ex-wife Robyn Wright; 23-year-old Dylan and 21-year-old Hopper.
