The thirteen-year-old son of Maria Shriver and Arnold Schwarzenegger is in the ICU unit of a Los Angeles hospital after a surfing accident Sunday.
People reports that Christopher Schwarzenegger was boogie boarding on Sunday, when something went wrong and he suffered a collapsed lung, broken bones and broken ribs. His mother was with him on the beach.
"Christopher has been in ICU since Sunday," a source tells PEOPLE. "Maria has not left his side and is sleeping at hospital."
On Friday, his older brother, Patrick, Tweeted an update, writing: "Thank you everyone for your messages about my brother. This kid is strongest kid I ever seen. Keep praying."
Christopher's father, Arnold Schwarzenegger, has also been visiting his son as well.