Attorney Greg Owen, who is representing four alleged victims, told ABC News students at the First Lutheran Church of Carson School would engage in oral sex during recess and nap time.
"It all boils down to a lack of supervision," he said. "There were times when teachers would let aides in the room for hours at a time to watch the kids. During nap time, the aides would be sleeping and the children would have been molesting each other during this time."
Owen said he plans to file a lawsuit Monday in Los Angeles County Superior Court against the school, the church, the principal, the teacher and the alleged child perpetrator.
KABC-TV, Los Angeles, reported one 5-year-old girl gave oral sex to at least two boys, aged 4 and 5 years old.
The father of the 5-year-old boy, Richard McCarthy, told KABC his son told him "about all the bad things that girl had been doing to him."
He said he's afraid to send his son to a new school because "the two boys that have been introduced to this feeling that they don't know how to process are still looking for it, and trying to make it happen."
"There's no way I can just take him to another school and be that parent that just lets a predator loose," he said.
Church leaders said the school closing has nothing to do with the alleged sexual activity, but is instead because of the recent resignation of the school director, who left for personal reasons, KABC reported.