Youth prisoner advocates have called on the Queensland government to lift the age of criminal responsibility to 14 or 15 instead of expanding the state’s overcrowded juvenile incarceration system.

They have also called for independent statutory oversight of a system they say relies overly on physical force, intimidation, isolation and “chemical restraints” of young prisoners and strip searches of girls who are overwhelmingly victims of sexual abuse.

The concerns are raised in submissions to a government-ordered youth detention review by the Youth Affairs Network of Queensland (YANQ) and advocacy group Sisters Inside.

On Thursday the government agreed to a request by reviewers – who were tasked with examining recent allegations of mistreatment of young prisoners, mainly in the state’s two youth detention centres – to expand the scope of their investigations to an incident in 2013.

This followed reported complaints by former staff at a youth prison in Townsville that they were not called to give evidence because their claims were outside the terms of reference.

A spokeswoman for the review said all submissions were considered, although those not called would have to apply separately for legal indemnity.

Queensland jails more children aged 10 to 13 than any Australian jurisdiction, almost 160 of a total youth prison population of 918 in 2014-15.

The United Nations considers holding children younger than 12 criminally responsible to be “not internationally acceptable”.

In its submission Sisters Inside called for the age of criminal responsibility to be raised to 14, saying that would cut the annual population of child prisoners by 18%.

That is more than the predicted influx of 17-year-olds soon to be removed from adult prisons, an issue that was raised in the wake of an alleged riot by 20 youth prisoners in Townsville last week. A guard was reportedly blinded in one eye after being struck by a projectile.

YANQ went further, urging Queensland to follow international “best practice” by adopting the Scandinavian model of 15 as the age of criminal responsibility and “welfare-based prevention” of youth crime.

It raised concerns about the prevailing use of medication to subdue undiagnosed teenagers in adult prisons.

On a visit to a prison in 2012, Queensland Health workers told YANQ that almost half the inmates were on medication, mostly antidepressants because “it keeps the order”.

Only 80 of 320 prisoners on medication – 30% of those aged 17 to 24 – were diagnosed with a mental illness.

More medication was given in a 600-bed prison than a 600-bed hospital, the health workers said, with $5,000 a month spent on the antipsychotic Seroquel when it was “not needed, it is just for them to sleep”.

YANQ also said it had heard claims of a culture of guards targeting young prisoners to break them into submission using unjustified force and intimidation, including late-night “raids” by guards in masks.

The raids included prisoners being “handcuffed, pummelled by officers, forced into stress positions [such as] hands on head ... kneeling for hours and [being] hit if [you] move at all”.

Fear of retribution means prisoners are “reluctant to make complaints”, with claims that “officers make changes to the complaint document themselves”.

A “culture of abuse and neglect of young people who end up on the margins of society [is] exacerbated in the youth detention and prison systems”, YANQ said.

“Young people quickly learn that they have to ‘cop it on the chin’ and not to make any complaint or ‘dog on anyone’. This culture of abuse leaves young people psychologically scarred.”

YANQ had raised complaints about mistreatment with prison management, “who not only did not deny it but openly stated these actions are necessary for an orderly management of the centre”, it said.

One parent contacted YANQ to say their son in jail had a hearing disability and guards were punishing him because they “think he is disobeying their directives”.

Queensland’s anti-discrimination commissioner was unable to intervene, YANQ said.

Sisters Inside said prison staff were “not adequately trained in strategies to manage behaviour that do not involve the use of force”.

It noted that of 172 children in youth prisons on an average day in 2014-15, 110 were Indigenous.

The number of Indigenous girls in prison annually rose over the previous three years from 69 to 109, a surge that explained why youth prisons “now operate almost permanently over accepted safe capacity levels”, Sisters Inside said.

It called for an end to strip searches, which were a “breach of human rights” and ineffective in finding contraband, citing only two significant discoveries in an audit of 41,728 searches over three years in the past decade.

Strip searches were especially traumatising for girls in prison, “almost all” of whom had been sexually assaulted, according to a document prepared by the Department of Justice and Attorney General in 2014.

“Some young women even report refusing visits from family members (including their children) due to the associated strip searching,” Sisters Inside said.

A former Brisbane youth prisoner, Nali, 19, told the group: “Even if you had your period, they still made you do it. If you say no, they just smash you to the floor. Three staff come in and they just hold you down and check you.”

Nali said she was once put in solitary confinement for a week after she obtained another prisoner’s Seroquel to help her sleep. She was forced to urinate in front of guards for drug tests and given four days’ extra isolation after she refused.

Both Sisters Inside and YANQ said the bail system was “broken”, with a lack of outside social support for young offenders a key problem. Children on remand rose from 66% in 2011-12 to 80% in 2014-15.

Denessa, 18, said: “I refused bail once. It was easier to be inside. It was fun, because there was no bullshit. And I didn’t have to see people I didn’t want to see. I got fed.”

YANQ said the transformation of Deception Bay, north of Brisbane, which in the 1990s had the highest rates of youth crime in Queensland, showed the value of targeted community support programs.

It said an estimated 0.04% of social welfare spending was on preventative and early intervention strategies in Queensland.