"They start out with a personality right off the bat," he said, adding that his son, Alexander is "a thug already."
"You saw him," he says turning to Matt Damon. "He's a moose! Literally, he just sits and he eats."
"He looks like he could bounce right now, some place in Hollywood," Damon said.
"Like, checking IDs on the way into the nursery," Clooney continued.
But if Alexander is of bouncer status, Clooney reveals his daughter Ella is a lot more demure
"She's very elegant, and all eyes. She looks like Amal, thank God," he said.
When it comes to the names though, the Oscar winner explains that he and his wife "just didn't want to have really dumb names."
"We figured these kids are going to be looked at a lot and watched and [have their] every move sort of judged, and we wanted them to at least have a break with the names," Clooney reasoned. "So we looked for some sort of normal names. We didn't have any great inspiration. It wasn't Alexander the Great and Ella Fitzgerald."
While Clooney had been preparing for fatherhood since finding out his wife was pregnant last fall, he admits that the idea that he would be a dad didn't sink in until they were born this past June.
"I suppose [the realest moment is] just the minute they came out," he said of fatherhood. "None of it is real until all of a sudden they're standing there covered in slime and crying. You're like, wait a minute, what is that? We were just two and now we're four."
"Everything changes pretty quickly," he added.
On Saturday, the 56-year-old actor made his first red carpet appearance at the film festival with Amal after welcoming their twins in June.
Photo Credit: Getty/ Jeff Spicer/Stringer, Getty / Valery Hache