Kate Hudson and Chris Robinson could teach some people—cough, Christie Brinkley and Peter Cook, cough—how to develop a friendly relationship postdivorce.

Hudson's ex-husband, Robinson, and her new man, Lance Armstrong, shared a coparenting outing on Wednesday morning at L.A.'s Palisades Tennis Center.

E! News has learned that Armstrong and Hudson, who split from Robinson in August 2006, have been taking their kids (Ryder, 4, and Armstrong's son Luke, 8, and twins Isabelle and Grace, 6) to a youth tennis camp all week long at the center in Pacific Palisades. Robinson and Armstrong care for Ryder "like a team," says a source.

Robinson and Armstrong took their kids to the tennis camp and, according to an eyewitness, they stood together during the teaching session and acted like "good buddies."

Says the source: "They're like one big happy family. They were just like two guys hanging out being totally cool with each other. If you didn't know the backstory, you would think they were just good pals."

How good? According to an eyewitness, Armstrong and Robinson were talking to the tennis center's owner Steve Bellamy, who also runs the Ski Channel and was Kate Hudson's tennis teacher when she was a kid. When Ryder hit a forehand, "they both cheered."

Sounds like a winning combination.