Sean Penn Is Adopting Charlize Theron’s Son Jackson

at 2:03 pm | By

Charlize & Sean to Wed?
The A-list couple reportedly have big plans together.
Sean Penn‘s family is about to get a little bigger.

The Milk actor has filed papers to adopt girlfriend Charlize Theron‘s three-year-old son, Jackson.

“Charlize and Sean are very serious,” a source close to Theron tells People of the Oscar-winning couple. “Charlize says this is it. Jackson already calls Sean daddy.”

The insider adds, “This is the first step toward them getting married.”

Penn, 54, and Theron, 39, have been dating for a year. Though there has been whispers of a secret engagement, neither stars have confirmed any plans of heading down the aisle.

A separate source tells Us Weekly that the duo are also planning to expand their brood even more.

“Sean always knew that to truly earn a place in Charlize’s heart, connecting with Jackson was one of the most important parts,” the Penn pal says. “There is still talk of adopting again and giving Jackson a brother or a sister.”

Theron adopted Jackson in early 2012 when he was 4 months old. He is her only child.

Meanwhile, Penn is the father of daughter Dylan, 23, and son Hopper, 21, from his previous marriage to House of Cards actress Robin Wright. The couple split in 2010.