"We were almost lucky, because it happened on a Friday morning, which is when we have our school assembly.
"By that good fortune I was able to talk to all of the kids about it. Not fear mongering or scaring them, but just giving them some strategies they can use."
The school has had no further reports of pupils being approached.
He said the school was part of the Keeping Ourselves Safe programme run by the New Zealand Police.
"The kids are well versed in this and the vast majority are picked up and dropped off by their parents," Watkins said.
"It does create mayhem here before and after school, but parents want to make sure their kids are kept safe."
Rotorua police area prevention manager Inspector Brendon Keenan said the suspicious activity had been reported to police and they had spoken with the young girl and her mum.
"Inquiries are ongoing and we will certainly monitor all other reports of suspicious activity.
"In particular, if they relate to that vehicle.
"We will be initiating any warnings as they come up, to the schools and to the wider community."
Any information can be given to Rotorua police on (07) 348 0099 or the anonymous Crimestoppers line on (0800 555 111).