UPDATE: Doting Dad Arnold Schwarzenegger and his daughter Christina visited Christopher in the hospital on Friday. The family has been by his side since the accident happened.
The 13-year-old's siblings took to their Twitter accounts Friday to thank followers for their well wishes and assure everyone their little bro is on the road to recovery.
"Thank you guys for ur concern and prayers for my baby brother! He's a tough little guy and getting better!" Katherine wrote. "Please keep praying for him! Xo"
"Thank you everyone for your messages about my brother," Patrick tweeted. "This kid is strongest kid I ever seen. Keep praying."
Christopher has been in hospital in a serious condition since last Sunday's incident.
He reportedly suffered a collapsed lung, broken bones and broken ribs while out in the ocean, which occurred while he was with his mother, Maria Shriver.