TV programmes should carry warnings at the start to stop children being exposed to inappropriate, violent or explicit material, headteachers have said.
More action needs to be taken to make sure that shows screened before the 9pm watershed are suitable for the audience and to prevent youngsters from witnessing adult themes, according to the National Association of Head Teachers (NAHT).
The call came as a poll revealed that nine in 10 parents want more regulation of programmes shown before 9pm, with a similar proportion (96%) saying that they believe that bad language and images of sexual and violent behaviour are on TV before this time.
The NAHT has launched a new charter which calls on schools, families, media providers and regulators to work together to keep unsuitable content away from children.
Amanda Hulme, head of Claypool Primary School in Bolton, who is proposing a motion on the charter at the NAHT's conference in Birmingham, said: "Schools and parents share concerns about the opportunities available to children to access inappropriate material.
"Parents should not feel alone in trying to hold back the tide of adult-themed content finding its way into their homes before 9pm or via internet-linked devices."
Speaking ahead of the conference, Ms Hulme said: "In the last couple of months there has been examples of inappropriate language before the watershed."
In one case, someone used the phrase "bloody hell" and in another "piss off" was used, she claimed.
Ms Hulme said: "I think that's completely inappropriate."
"If I used either of those phrases in school, either in assembly or in front of a group of children there would be serious repercussions."
Ms Hulme said that TV programmes should carry warning to help parents decide whether a show is suitable for their child.
"If it just said that there was reference to inappropriate language, or even just better information for parents before a programme starts," she said.
She added: "At least as a parent you would have that choice to say 'we'll record it or we'll watch something else'.
"It's very easy when you're sat there and you think everything's fine because it's pre-watershed and then suddenly there's a theme, or there's some words that are used and you think 'I'm not sure if I'm happy with my child listening to that'."
In her speech to the conference, NAHT president Gail Larkin is also due to warn that children need to be protected from being exposed to potentially "obscene and mentally damaging material".
Ms Larkin said: "As school leaders, we are committed to 'letting children be children'.
"We strive to ensure that our children are happy, safe and secure when they are in school.
"We also know that most parents are trying to do their best to protect their children from certain dangers in the outside world but I know, as a grandparent, how much more difficult it is in this age of such advanced technology to prevent children from accessing, often unwittingly, materials and media that are not just inappropriate but often obscene and mentally damaging."
According to regulator Ofcom's guidelines, there are strict rules about what can be shown on TV before the 9pm watershed.
The guidance says that unsuitable material that should not generally be shown before this time includes "everything from sexual content to violence, graphic or distressing imagery and swearing".
It adds: "For example, the most offensive language must not be broadcast before the watershed on TV or, on radio, when children are particularly likely to be listening. Frequent use of offensive language must be avoided before the watershed, and must always be justified by its context."
An Ofcom spokesman said: "The protection of under 18s from inappropriate material is a fundamental concern for Ofcom. There are clear broadcasting rules designed to protect children, which we actively enforce.
"We recently issued new guidance on the TV watershed, warning broadcasters to be more careful about programmes they show before 9pm that could be unsuitable for children."
"We constantly monitor audience attitudes and our research shows that the vast majority of adults believe the current level of TV regulation is about right."
:: The NAHT poll questioned 1,013 parents of school-age children living in England, Wales and Northern Ireland in January.