Police said the child and her mother were visiting friends at a second-floor apartment on Sullivan Street.
They said the little girl and her 3-year-old friend were bouncing on a bed when the 4-year-old went through a screen and fell to the pavement below.
She was rushed to University of California Irvine Medical Center with serious head injuries, but she is expected to survive.
Police are calling it a tragic accident, but the incident remains under investigation.
