PHILADELPHIA (CBS) — Police are investigating an incident that occurred at Meade Elementary School in North Philadelphia on Tuesday, after a 7-year-old student said she was poked with a hypodermic needle.

The girl said another classmate stabbed her in the back with it.

Authorities said she did go to the hospital and no visible marks or wounds were found.

The school’s principal, Raqueebah Burch, sent a letter home with students, informing parents that a hypodermic needle was brought into the school and that some children came in contact with it.

But now some parents say they don’t want to send their kids back to school until the situation is resolved.

Christina Marshall found out her 7-year-old son Christian had witnessed the incident when the principal called.

“He was nervous. He thought he would be in trouble for not telling,” Marshall said.

Christian says he saw another student in his class pull four needles out of a backpack and hand three to other students.

“I saw a needle. She was like, ‘this will keep y’all away’,” Christian said.

It’s not clear if the student was chasing others or if students were stabbing themselves.

Philadelphia School District officials say they are also looking into the matter.