A child's caretaker discovered the discarded blades at the recreation area in the 2400 block of Park Boulevard about 2:45 p.m., according to San Diego police.
Officers cordoned off the facility and used a metal detector to search the grounds for any other blades. None were found, Officer Dino Delimitros said.
It was not immediately clear when the play area would reopen to the public.
On several occasions in recent years, people have been injured at several local parks by razor blades maliciously planted in lawns by unknown malefactors.