"It's chaos at times, but there's such joy in the house," the Curious Case of Benjamin Button Oscar nominee, 45, tells Britain's Daily Telegraph.
"I look and there's our boy from Vietnam [Pax, 5] and our daughter from Ethiopia [Zahara, 3], and our girl was born in Namibia [Shiloh, 2], and our son is from Cambodia [Maddox, 7], and they're brothers and sisters, man. They're brothers and sisters and it's a sight for elation."
Not to mention twins Knox and Vivienne, born last July in France.
"We were four before, and we got into our rhythms and it worked. Then someone new comes in, and it discombobulates the movements for a moment, but then you settle in again and it just all works," he tells the paper. "Everyone's pretty well integrated. It's not the first time new kids have come in.
"We have the capability to give a child a home, and let me tell you it's selfish, too, because the reward has been extraordinary."
Brad's Love for AngelinaIn the case of the twins, the fun and the chaos come in a double dose.
"One seemed simple, and it's just double the fun. It's surprising how soon their personalities have started emerging. But it's really important that everyone gets their individual time as well as group time together," he says.
That includes partner Angelina Jolie.
"Angelina and I are together because we can enhance each other," says Pitt. "I don't want to waste any time because I'm with company I really, really love."
Brad & Angelina welcome Knox & Viv!
2005: See photos from Brad & Angelina's first vacation together