A West Dorset school sent emails to parents after both Dorset and Somerset children’s services have told schools of the potential dangers.
Deputy headteacher of Beaminster School, David Withers, said: “We wanted to raise awareness rather than be alarmist.”
Mr Withers told parents police have been following a case in Somerset where adverts displayed in newsagents for babysitting help turned out to be a method of making contact with a young person potentially for grooming purposes.
He said: “Police followed up a situation in which the person placing the advert requested to meet with the young person beforehand.
“Fortunately the young person arranged this meeting in a public place and took a parent along.
“The advertiser failed to turn up but had clearly been there and seen that the young person was accompanied by an adult.
“They tried to arrange another meeting.
“This particular person was a registered sex offender.
“We will speak with our older pupils about this risk and advise them of how to ensure they keep themselves safe when applying for jobs advertised in shop windows, but we felt that parents should also be made aware.”
Former parent governor Paula Buxton, who runs Beaminster’s youth centre, said: “I have been told since the email by a couple of people that their kids have heard of kids who have offered their services to people without really looking into who they are going to babysit for.
“Sometimes teenagers think babysitting is something they can do but don’t recognise possible dangers. Parents need to be as aware as well as the youngsters.”
She added: “They are in someone’s house, someone they might not know that well – or even if they do know them well, how safe are they? These days you can’t be sure of anything.
“Police checks may be too extreme but there needs to be something.”