One Scottish parent told the charity they were only prompted to speak to their 16-year-old daughter after finding “an inappropriate image on her phone”.
Another said they spoke up following an awareness day at school.
The number of children counselled by Childline about sexting has risen 15% to almost 1,400 - around four a day - in the last year.
Nearly two-thirds of parents have not spoken to their child about sexting, a UK-wide survey of 1,000 parents found. More than a quarter of the survey’s participants live in Scotland.
Almost half of parents did not not know it is illegal for anyone under 18 to take nude selfies, the NSPCC said.
More than a third of parents fear their children will be involved in sexting and around a quarter said they were concerned about their child losing control of the image.
Matt Forde, head of service for NSPCC Scotland, said: “Sharing nude selfies can put young people at risk of bullying by peers or being targeted by adult sex offenders, so it’s vital that parents talk to their children and that young people feel empowered to say no to sexting requests.
“We realise that talking about sexting can be an embarrassing or awkward conversation for both parents and children.
“Although most parents said they would seek help if an indecent image of their child had been shared on the internet, half of them weren’t confident about getting the right support.
“The NSPCC has created a new guide for parents to help them talk to their children about the risks of sexting, what the law says and what to do if their child has shared a nude image that is being circulated online or among their peers.”