Gwyn and Ben: Still Friends

Exes Gwyneth Paltrow and Ben Affleck have stayed so close since their two-year relationship ended in 1999 that even their kids are pals!

Ben and his daughter Violet, 4, joined guests, including Steven Spielberg and Liv Tyler, at an April 11 rodeo-themed 3rd birthday for Gwyneth's son, Moses, at the actress' L.A. home.

With wife Jennifer Garner noticeable absent, State of Play star Ben, 36, chatted with the actress-turned-lifestyle guru, 36, while their children played.

"They had a lot of games for the kids, including a real horse with a cowboy," an onlooker tells OK!.

But did the reunion upset Gwyn's hubby, Chris Martin? The bashful 32-year-old rocker ducked into the house when he saw Ben arrive.

"Chris didn't want to be around," adds the spy. "As soon as Ben left, he came back out."