Most parents believe sexting is potentially harmful - but nearly six in 10 have not spoken to their children about the issue, according to new research.
The finding emerged in a survey by the NSPCC, which warned that sharing nude selfies can put youngsters at risk of bullying or being targeted by paedophiles.
Nearly three quarters (73%) of the 1,000 parents and carers interviewed across the UK thought sexting is "always" harmful.
The most commonly cited worry was the danger of the child losing control of the image, which was raised by one in four of those surveyed.
Very few mothers and fathers believed their child had sent a sexual image or video of themselves, but around two fifths were concerned that they may be involved in sexting in the future.
When asked if they had ever spoken to their offspring about sexting, 39% of respondents said they had not but intended to, while 19% had not and did not intend to. Two in five had spoken to their child about sexting at least once.
NSPCC chief executive Peter Wanless 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.
"And 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 trend for sharing explicit images among youngsters has emerged as a challenging issue for authorities following the explosion in smartphone ownership, with warnings that it can leave teenagers vulnerable to exploitation or blackmail.
Last year it was disclosed that child protection officers are probing one case involving the practice every day, while figures obtained by The Sun showed hundreds of under-18s have been investigated for sexting.
The survey suggested there is uncertainty about the law in relation to sexting, with parents split on whether or not it is illegal for a child to take nude selfies.
Under the letter of the law making or sharing indecent photographs of anyone aged under the age of 18 could be classed as an offence - but there have been calls for recording rules to be adapted so children are not routinely criminalised.
In one reported episode a 14-year-old boy was added to a police database after he sent a naked image of himself to a female classmate on picture messaging app Snapchat.
The NSPCC revealed that in the last year the number of children counselled by Childline about sexting has increased by 15% to almost 1,400.
A 17-year-old boy who called the service said: "There are definitely risks involved. Someone saw a video message I had sent to a previous girlfriend, took a screen shot and posted it online. They called me a pervert and lots of people I knew saw it - it was clearly me pictured.
"I was completely devastated and, to be honest, almost suicidal. I got the picture taken down eventually, but by that stage people had 'unfriended' me and the damage was done."
The NSPCC has created advice for parents on talking to their children about sexting.
A Department for Education spokeswoman said:"Everyone has a role to play in protecting children from the risks they might face either online or on their phones.
"By working with parents, schools and network providers we can educate children on the risks of sexting.
"This new advice will support the updated guidance that schools will be using from September to help talk about this issue with pupils and their parents."
::The NSPCC advice is outlined at www.nspcc.org.uk/sexting