The two umbrella organisations representing the world's religious orders issued a joint statement ahead of Pope Francis's sex abuse prevention summit, which opens on Thursday.
They vowed to implement accountability measures going forward to ensure that cover-ups by religious superiors end and that children are always safe in the presence of clergy.
With a few exceptions, religious orders have largely flown under the radar in the decades-long scandal, since the focus has been on how diocesan bishops protected their priests and moved them from parish to parish where they were free to abuse again.
Yet congregations such as the Jesuits, Salesians and Christian Brothers have some of the worst records, since they too moved abusers around and had easy access to young victims, as many orders specialise in running schools.
The Union of Superiors General represents the leadership of male religious orders, which count around 133,000 priests globally.
The female branch, the International Union of Superiors General, represents some 500,000 religious sisters.
They will each send around a dozen representatives to the Vatican sex abuse summit.
In the statement, the groups said they were ashamed at how they had failed the most vulnerable they were meant to serve and blamed "the strong sense of family" that their communities fostered for having blinded them to the warning signs.
"It resulted in a misplaced loyalty, errors in judgment, slowness to act, denial and at times, cover-up," they said.
"We still need conversion and we want to change. We want to act with humility. We want to see our blind spots. We want to name any abuse of power."
To that end, the statement also condemned recent revelations of priests and bishops who sexually abused seminarians and nuns - an abuse of power that has largely gone unpunished since the victims are adults.
While noting the pope's summit is focused on the protection of minors, the groups pledged to find a response.
"This is a matter of grave and shocking concern," they said.
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