Children aged two or younger are being allowed to use the internet, while many youngsters are spending much longer online than their parents realise, a new poll suggests.
The survey reveals that almost four in five children (79.8%) have seen images or information about eating disorders and self harm on the internet, and more than two in five (42.1%) admit that they have seen online porn.
Others have seen content on suicide, child abuse, animal cruelty, gambling, terrorism or cults.
In many cases, children accidentally accessed this inappropriate content, but almost one in 10 (9.4%) revealed they found it on purpose because they were looking for it, while a further 18.1% found it by following links they were curious about.
The Netmums survey questioned around 1,100 parents and about 825 children aged seven to 16 for their views on the internet.
The findings show that three quarters (72.8%) of parents believe that their child spends under an hour a day online.
But an analysis of the children's poll suggested that on average, youngsters are spending two hours each day on the internet, Netmums claimed.
Around one in eight (12.8%) of the parents surveyed said that their son or daughter was two years old or younger when they were first allowed to go online, while 16.7% said that they let them use the internet at age three.
The survey also found that almost three in 10 parents (29%) let their youngster use the internet without any restrictions or supervision.
More than three quarters (77.1%) of the children questioned said that they had not acted on information they had found on an inappropriate site. But 17.3% said it made them think about acting on it, while 5.4% said they tried to restrict their eating, 3.4% self-harmed and 2.1% considered suicide.