Jaymisha Pires and Corey Granberry, both 21, spotted the man cutting his 8-year-old son with a glass shard Saturday at the Mount Hope Cemetery in San Diego.
Granberry told KGTV-TV, San Diego, the man, identified as Joseph Ramirez, 30, of San Diego, said, "I want to sacrifice him. He needs to go with grandma or mom ... ."
Pires told U-T San Diego her "motherly instincts kicked in" and she kept pleading with him to release the children.
"He was like, 'No, these are my kids. We're going to Jesus,'" Pires said.
Ramirez, who said he was hearing the voice of his dead grandmother in his head, initially let the other two young children go and then finally shoved the boy to the side and ran.
Dana Fontenot a 60-year-old security guard who was just in his third day on the job at the cemetery, talked Ramirez a short distance away.
"It's all in a day's work," Fontenot told the newspaper.
The boy was treated and released from a hospital. Ramirez was being held in the San Diego jail on suspicion of attempted first-degree murder and cruelty to a child. He is to be arraigned Wednesday.