The 7-year-old boy, identified in the suit only as "EF", is in treatment again as he battles stage 4 neuroblastoma, a rare and aggressive form of cancer, which his parents say has returned three times.
Timothy and Linda Wratten said their anxieties and concerns about their son's health increased when his stem cells harvested in 2014 were lost. They would've been used as part of his treatment.
"The freezer failed and the previous stem cells of EF and 55 other brave children battling cancer were destroyed," said Adam Wolf, the family's attorney.
The Wrattens say they learned about last year's malfunction through social media.
"I found it even more shocking that, not only were we part of this disaster, we weren't even properly notified," Linda said.
Children's Hospital L.A. issued a statement which reads, in part: "We remain deeply sorry for the loss of blood stem cells resulting from the failure of a freezer...and we apologize for the mishandling of outreach to the affected families."
The hospital also said that "should the need arise," more blood stem cells could be collected at no costs to the families.
But the Wrattens say they've been told it would be a miracle for the medical team to harvest stem cells again.
"His bone marrow is essentially damaged from all the treatment he's received," Linda said.
The hospital says it has replaced the freezer that malfunctioned and has upgraded its sensor monitoring and alert system.