Arnold Schwarzenegger and Maria Shriver's son is in intensive care.

Christopher Schwarzenegger, 13 - the youngest son of the estranged couple - was injured while boogie boarding in Malibu, California on Sunday (17.07.11), suffering a collapsed lung and multiple broken bones according to TMZ.

Maria was with her son when the incident occurred and has been keeping a vigil over him while he is being treated.

A source told People: "Christopher has been in ICU since Sunday. Maria has not left his side and is sleeping at hospital."

Arnold has also visited Christopher in the hospital.

Despite initiating divorce proceedings after discovering the 'Terminator' star fathered a boy named Joseph with their family's housekeeper Mildred 'Patty' Baena 13 years ago - around the same time as she had Christopher - Maria has tried to keep her split with Arnold as amicable as possible for the sake of their kids.

The former news anchor - who has four children, Katherine, 21, Christina, 19, Patrick, 17, and Christopher with the former Californian governor - is set to buy a $10 million home in the Los Angeles district Brentwood, which is just down the road from her former marital home so it's easier for the custody arrangements of their two younger children.

An insider said: "This is going to be a very amicable divorce, and it won't be played out in the media. Neither one of them wants that. Arnold hasn't lost his mind, he is going to be giving away his Fortune to her. He wants to show his children that he is taking responsibility for his actions."