Bad language and sexual images are being aired before the 9pm television watershed, according to 96 per cent of parents polled by the National Association of Head Teachers (NAHT).
According to the Research Now survey, nine in ten parents want more regulation of pre-watershed TV.
Of 1,013 parents of school-age children, more than 80 per cent said childhood is under threat largely due to kids’ early exposure to adult themes.
It also revealed that 85 per cent of parents are concerned that such material can begin to be accepted as normal by children who see it regularly.
It comes as the NAHT proposes a charter which calls for the media to be more careful around programmes before 9pm and for school leaders to tackle the issue firmly.
Media campaigners have also raised concerns about the watershed as catch-up TV services are increasing in popularity.
Vivienne Pattison, of Mediawatch-UK, said her young child “has no concept” of only watching programmes when they are aired.
Reg Bailey, who leads the Mothers’ Union and has worked with the Government on similar issues, gave his support to a ratings system similar to that used for films instead of the 9pm watershed.
Both Channel 4 and the BBC pointed to their systems of parental locks for programmes on their on-demand services.
Ofcom, which is the communications watchdog but cannot legally enforce a watershed on catch-up services, said the 9pm cut-off “is an important way to protect children”.
Tony Close, director of content standards at Ofcom, added: “We are working with government to ensure that children remain protected.”
The Department for Culture, Media and Sport said more was needed to ensure catch-up TV parental locks are more widely used.
It commented: “We will keep progress under close review and if necessary consider the case for legislation to ensure that audiences are protected to the level they choose.”