The boy appears to have been the intended target.
He remains in critical condition.
No one else was hurt.
Officers said gang slogans were heard at the scene.
Anyone with information is asked to call the Fullerton police gang unit at (714) 738-6715.
Police continue search for boy's shooter
FULLERTON, Calif. Authorities said the boy was with friends near Topaz Elementary School in the 3200 block of Topaz Lane at about 8 p.m. when someone approached the group and opened fire.
