Arnold and Maria with their four kids at his 2003 inauguration: Christopher, then 6, at left, with Patrick, Katherine and Christina. (Hector Mata/AFP/Getty Images)

The details of the accident are unclear, but TMZ reported that Christopher Schwarzenegger, 13, suffered a collapsed lung and broken bones in the incident Sunday. People reports that Shriver was on the beach in Malibu, Calif., with her son when he was injured while boogie-boarding, and that she’s spent all week in the hospital with him.

Read earlier: The Schwarzenegger-Shriver divorce: How rich is Maria Shriver?, 7/6/11

Schwarzenegger’s love child: how did he keep the secret so long?, 5/18/11

Arnold Schwarzenegger and Maria Shriver, a political couple “in transition” after 25 high-profile years (photos), 5/10/11