National Society for the Prevention of Cruelty to Children (NSPCC) urges that new computers should carry high-security "blocking" software that stop them from viewing violent or sexually explicit pictures.
The recommendation came after a child posted a comment on the message board of the NSPCC's website There4me.com saying: "I've seen violent images I didn't search for. I was freaked out."
Another said his eight-year-old sister typed in "pictures of animals" and got pornography adverts.
"We are alarmed by how easy it is for children to access disturbing internet material," the Sun quoted Policy adviser Zoe Hilton, as saying.
"High-security parental controls in computers would help shield them.
"We also want retailers to ensure computers have protection software before they are sold to parents," Hilton added.