Papua New Guinea officials have been unavailable for comment on claims police officers routinely beat children in custody.
The New York-based group Human Rights Watch says police use guns, bars, batons, hoses and chairs to beat children.
The report also alleges PNG police often rape women, men, girls and boys, in custody.
The group's children's rights researcher Zama Coursen-Neff, says police violence is standard practice and much of that violence is against children.
"We've found that police are often picking up girls and young women, raping them and then letting them go again. We also found that there is police rape of women and girls in cells, and that's actually something that was admitted to me by the head of the internal affairs department of the police force."
Zama Coursen-Neff says men and boys are also targeted for homosexual rape.