The 'Fury' star is reportedly "much happier" now he has been able to see his kids – Maddox, 15, Pax, 13, Zahara, 12, Shiloh, 10, and eight-year-old twins Knox and Vivienne – more often as they are his "whole world".
A source said: "He seems to have a more positive outlook. Things seem much better now ... He can spend more time with them ...
"He seems much happier. He has missed his kids terribly. The kids are his whole world. It's all he cares about."
And the 53-year-old actor is happy to work with his estranged wife in the hope it will make the split easier on their children.
The insider added to People magazine: "Brad is willing to work with Angie so they can have peace for the kids. What it ultimately comes down to is that he just wants to be with the kids."
It comes after Brad and Angelina agreed to resolve their divorce and custody dispute in private.
They announced in a joint statement: "The parties and their counsel have signed agreements to preserve the privacy rights of their children and family by keeping all court documents confidential and engaging a private judge to make any necessary legal decisions and to facilitate the expeditious resolution of any remaining issues. The parents are committed to act as a united front to effectuate recovery and reunification."
And Brad is thought to have moved back into the family home in the Los Feliz estate after neighbours confirmed they had seen him "there most days".
A source said: "Brad wants to prove to the courts that he's putting the children's welfare first.
"Obviously the family circumstances have changed dramatically, but he wants them to feel at home there. He's doing everything he can to try and fight or his kids."