"Your child's safety is of paramount importance. Please remind your child about safe walking in pairs or small groups," he wrote in the email.
Hill told the Herald the first approach happened on Tuesday morning, and a second on Thursday evening after school.
A third sighting of the man was reported this morning when a staff member saw him lurking on school property.
"I have emailed the school community and surrounding local primary schools," Hill said.
"We need to remind parents to talk to their children about walking in pairs, and taking the most direct route to and from school.
"We have also alerted local police, who will increase their presence in the area."
The Herald has approached the police for comment.