It’s only been six months since Rooney Mara and Joaquin Phoenix quietly welcomed their first child, but a friend says the blissed-out couple is already about growing their family. 

, 35, and , 46, who were spotted out and about with their boy, River, in L.A. on February 26, “both knew becoming parents would be great, but they say it’s the best thing that’s ever happened to them, especially ,” the pal spills to OK!, adding that having this little family has “exceeded all their expectations.”

The couple named their son after the Joker star’s late brother, who tragically died of a drug overdose in 1993 at the age of 23. “It’s been healing for Joaquin in a way he could never have imagined,” shares the friend. 

Currently, the two are living in the Hollywood Hills neighborhood, along with their two dogs named Oskar and Soda, and tend to stay out of the public eye. 

“They don’t really like to go out,” an insider told Us of the private pair. “They mainly just like to be with each other as the two of them. They’re in their own bubble.”