"She saw them taking off their clothes and that she saw them doing personal things to each other, the students," a concerned grandparent said.
The woman's 7-year-old grandchild was the one who told a teacher's aide on Wednesday about the two incidents, one of which was oral sex between the two students.
It is the kind of thing no parent could ever imagine. The first reaction is shock that this could happen in their child's school.
"If I had known this morning, I would not have brought him to school," parent Lataya Young said.
Another reaction has been, "Where was the teacher?"
"The teacher should have paid more attention to what's going on," parent Nikki Turner said.
School officials believe the teacher was in the room, but that is all he could tell them.
"He expressed that he did not have any knowledge of what is alleged to have occurred," Oakland Unified School District spokesperson Troy Flint said.
On the minds of most everyone is how children could so young know so much?
"I don't understand it, but it's on the parents, OK, because they learn that at home, they don't teach that at school," Allen Saunders, who's nephew is in the class, said.
"This is profoundly abnormal behavior," pediatrician and child abuse expert Dr. Jim Crawford said. "My concern would be maybe something happened to one or more of the kids involved and that they're responding in this type of behavior because of what happened to them."
These are all things that Oakland school police are investigating. Assisting them are investigators from the Oakland Police Department sexual assault unit, who were talking to the 20 or so children in that classroom.
The grandmother of the girl who reported the incident says the principal gave her an award and that her family raised her well.
"She knows right from wrong and I'm very proud of her," she said.
The district has been providing counseling for the children in the classroom and the principal has been speaking with students. The district has not released the teacher's name but he has been placed on administrative leave.