The school's nurse examined the children, and officials alerted their parents, police said.
Although police said there was no needle on the syringe, one victim's mother, Amanda Sappia, told KTVK that she believes it may have snapped off at some point.
"Being subject to a used needle, it's just scary," Sappia told KTVK. "You don't know what that person had, if they had any contractible diseases or anything."
Police are trying to determine where the boy found the syringe. He will not be charged, KPNX reported.
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