Concerns about a child's sexual behaviour - including sexting and sharing sexual images - should always be followed up, a watchdog has said.
New guidance from the National Institute for Health and Care Excellence (Nice) also calls for professionals to consider involving a child's family before intervening.
It lists sexual behaviours which may be inappropriate for the child's age and to which teachers, nurses and social workers should be alert - but urges them to avoid stigmatising the child.
Behaviours include using sexualised language such as adult slang to talk about sex, viewing pornography and sexualised behaviour such as sexting or sharing and sending nude images by mobile phone or email.
The guidance says that while these behaviours should not be ignored, many children will naturally grow out of them.
Professionals should "focus on the child or young person as an individual and not on the presenting behaviour" and "recognise that inappropriate sexualised behaviour is often an expression of a range of problems or underlying vulnerabilities".
Figures released earlier this month showed that more than 2,000 children were reported to police for crimes linked to indecent images in three years.
The National Society for the Prevention of Cruelty to Children (NSPCC) submitted a Freedom of Information request to police across the UK, which revealed that a total of 2,031 under-18s were reported for crimes linked to the possession, distribution, or production of indecent images of children in 2013, 2014 and 2015.
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 incident, 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 new Nice guidance recommends professionals use the Brook Sexual Behaviours Traffic Light Tool, which lists sexual behaviours by age group to say whether they are normal or need further investigation.
It also calls for further research into the impact electronic media is having on sexual behaviour.
Jon Brown, head of development and impact at NSPCC and a member of the Nice guideline development group, said: "Harmful sexual behaviour has gone under the radar for too long.
"There are three key messages in this guidance: that children and young people should be treated as just that, not as mini sex offenders; that the approach should be shaped to the individual, it's not a one size fits all process; and, finally, that steps to change behaviour will only be effective if the family and support network understand there is an issue and are supportive."
Professor Gillian Leng, deputy chief executive of Nice, said: "Inquisitive behaviour is a normal part of growing up and it is natural for children to ask about different body parts or be curious about the differences between girls and boys.
"However, there is also a minority of children and young people who engage in sexual behaviour that is not appropriate for their age or development.
"This guidance is about preparing teachers, nurses, social workers and others to recognise harmful sexual behaviour when it occurs and ensure they can work across team boundaries so that problem behaviour is not ignored or missed and children and young people receive the help they need."
Anne Longfield, Children's Commissioner for England, said: "It's important that a range of professionals recognise and know how to effectively respond to this kind of behaviour, which can be challenging – and understand that some children may themselves be suffering abuse or exploitation so that appropriate action is taken."