Anaheim Police Lt. Bob Dunn says a mattress was found inside the large kennel-like cage.
An anonymous caller tipped off authorities Tuesday night.
Dunn says the child was not in the cage when officers arrived, but there are varying reports that he may have been kept inside it for several months, and even years.
Dunn says the boy is physically in good shape.
Two other children, ages 8 and 10, were also taken from the home.
The boy's father, 40-year-old Loi Vu, and his mother, 35-year-old Tracy Trang Le, were arrested on suspicion of child endangerment and false imprisonment. It wasn't immediately known if they have a lawyer.