And then, Mark Berndt photographed them, creating hundreds of images that would eventually lead to his arrest, police say.
On Tuesday, Berndt, 61, was sitting in jail on charges that he committed lewd acts on 23 boys and girls, ages 6 to 10, between 2008 and 2010. None of them complained about Berndt's behavior, authorities said.
Police and school officials only learned of it when a film processor found Berndt's photos more than a year ago. Since the discovery, the school district fired Berndt and police put him under surveillance.
"If it wasn't for the film processor, this could still be continuing today," said Lt. Carlos Marquez of the Los Angeles County sheriff's department.
Berndt was arrested Monday at his home in Torrance and was being held on $2.3 million bail.
Some parents picking up their pre-kindergarteners at the school on Tuesday complained that officials at Miramonte Elementary School in South Los Angeles should have notified them when the photos were found.
"My concern is why, if the principal knew this in advance, why didn't he inform us?" said Gloria Polanco, the mother of a second- and a third-grader. "How long has he been doing this?"
The probe began after the film processor, who is required by state law to report suspicions of child abuse and molestation, turned over some 40 photographs to authorities.
About 400 photos were found at Berndt's home and at the photo lab during subsequent searches. It's not clear how many different children were pictured. At least 10 youngsters in the photos have not yet been identified.
Some photos showed Berndt with his arm around children or his hand over their mouths. Some photos showed children with live bugs the size of hissing cockroaches on their mouths or faces.
Others depicted girls with what appears to be a spoon up to their mouths as if they were going to ingest a clear-white liquid. Children were fed Berndt's semen from a spoon or on cookies, Marquez said.
Kids reported being fed something distasteful. A blue plastic spoon and container found in the trash in his classroom tested positive for his semen, authorities said.
Police recommended the children in the photos be tested for sexually transmitted diseases. There also may be more victims given the length of time that Berndt taught at the school, Marquez said.
Authorities could have arrested Berndt on misdemeanor charges when the investigation began but chose to build a stronger felony case, Marquez said. He could get a life sentence if he is convicted.
At first, neither the parents nor the children believed they had been molested, so there wasn't much reaction, according to sheriff's spokesman Steve Whitmore. It was only after the matter of the semen was raised that they became alarmed.
Berndt, who has no previous arrest record, was placed under surveillance and is not believed to have had contact with children during the investigation. The childless bachelor lives a few blocks from two parks and an elementary school.
As for surveillance of Berndt, Whitmore said, "It was routine. It wasn't 24-7. We knew his whereabouts. We checked information to make sure he wasn't connected to the Boy Scouts, the YMCA, wasn't a camp counselor, anything that would bring him in contact with kids. He wasn't."
The incidents occurred during school hours but not all the children were his students, Marquez said.
"The reason some of the kids are not his students, per se, is that during the lunch breaks or recess, he'd go out to the playground and entice them back to the classroom," Marquez said.
"They didn't know they were being violated in that manner," he said. "They just thought it was a game."
Berndt was a teaching assistant in the Los Angeles Unified School District in 1976 and 1977 and he began teaching at Miramonte in 1979, according to a district work history obtained by the Los Angeles Times.
Berndt had no disciplinary actions on file and performed up to standards in his last five evaluations over the last decade, according to the document.
Miramonte Principal Martin Sandoval said he wanted to express his sympathy to the children's families.
Los Angeles Unified School District Superintendent John Deasy said in a statement that he was notified of the investigation last January and removed Berndt from the classroom the same day. The school board then fired him, he said.
While Berndt may be long gone from the school, the incident has left its mark.
"My children won't be coming back here," said Kimberly Kirklin, whose teenage daughter was in Berndt's class three years ago. "He preyed on our innocents. He tainted a whole neighborhood."
Berndt is scheduled for an arraignment Wednesday in Los Angeles Superior Court. He has hired a lawyer and has made no statements to authorities, Whitmore said.