The School of Rock star spent time playing games with patients at their bedsides and talking to their families during the special visit.

The Tenacious D rocker also joined in on several music therapy sessions for the children, leading patients in rousing renditions of The Lion Sleeps Tonight and Twist and Shout.

The Children's Hospital Los Angeles is the first and largest pediatric hospital in Southern California, and this is its second annual month-long Make March Matter campaign, in support of children's health.

Jack joins fellow celebrities like Natalie Portman and Kim Kardashian in visiting the medical centre, and Oscar winner Natalie even penned an essay describing her experience volunteering at the hospital.

"I'm impressed by the programs and positive environment the hospital provides for so many kids and their families," she previously wrote for InStyle. "It has created support systems that are social as well as medical, so when I volunteer, I'm able to play games like Uno, Scrabble, Wii Sports, and more with the kids to help lift their spirits."

"I'm happy to work with a fund-raiser that partners with local businesses to assist these families," she continued. "When we're in a position to alleviate some suffering, I believe we should."

Reality star and mother-of-two Kim recently volunteered at the Children's Hospital to launch their Make March Matter campaign.