Calls have been made for security to be installed to prevent violent or sexual content being seen by children.
The NSPCC polled visitors to its children's website there4me.com and revealed that 377 of 497 votes cast claimed to have been disturbed by internet images.
The charity has renewed its call for computer manufacturers and retailers to install security to prevent these images being found. It has also called for social networking and video hosting sites to remove offensive material within hours of finding it.
NSPCC policy adviser Zoe Hilton said: “Children are just a few clicks away from innocently stumbling across upsetting or even dangerous pictures and films such as adult sex scenes, violent dog fights, people self-harming and children being assaulted.
“High-security parental controls installed in their computers would help shield them. Currently computer manufacturers and retailers leave it to parents to find and install software that filters out material unsuitable for children. This can be a complicated process for customers.
“Social networking sites must also put more effort and resources into patrolling their sites for harmful and offensive material and ensure their public complaints systems are clearly marked, easy-to-use and child-friendly.
“We would also recommend they give information on their sites about sources of help and advice, such as Childline, for children who have been affected by what they have seen.”