Arnold Schwarzenegger and Maria Shriver's son Christopher in ICU after surfing accident

(CBS) Arnold Schwarzenegger and Maria Shriver's 13-year-old son has been hospitalized in serious condition following a surfing accident last weekend.

Christopher Schwarzenegger was boogie boarding on a beach in Malibu, Calif., when the accident occurred, according to reports. He suffered a collapsed lung, broken bones and broken ribs and is in the intensive care unit.

Pictures: Maria Shriver
Pictures: Arnold Schwarzenegger

A source told People magazine that Shriver was with him on the beach.

"Christopher has been in ICU since Sunday," a source told the magazine. "Maria has not left his side and is sleeping at hospital."

TMZ reported Friday that the 13-year-old's condition has been upgraded and he will be OK.

Schwarzenegger has also been a regular visitor at the hospital, according to the website.

Christopher is the youngest of the couple's four children. They are also parents to Katherine, 21, Christina, who turns 20 on Saturday, and Patrick, 17.

Shriver filed for divorce from Schwarzenegger earlier this month, following the couple's separation after revelations that the former California governor fathered a child out of wedlock.