The 52-year-old actor bonded with his 'Gravity' co-star's four-year-old little boy, Louis, on the set of the space drama in 2011 and despite regularly making jokes about his actress pal, 49, George thinks she is a ''really, truly fun'' mother.
'The Monuments Men' star told PEOPLE.com at the New York premiere of the film: ''I haven't babysat Louis, but I've spent some time with that kid. He's a good kid. Sandy - I don't know. But the kid's good!''
He added: ''Honestly, I can make all the jokes I want about Sandy because I love her, but she's an unbelievable mom. And that kid's unbelievably great.''
The Oscar-winning actress, who adopted Louis in 2009, previously revealed that Louis was a huge fan of George and demanded to spend quality time with him alone away from the set.
She said: ''My son thinks he's a very cool dude. If there's a choice between me [and] George and Alfonso [Cuaron, the director], my son will leave me to be with George and these guys. He's a boy's boy, so he has to go talk to the men.''