Some children have been plied with drugs or alcohol and trafficked around Northern Ireland in taxis for sexual exploitation, senior police said.
A total of 22 suspected grooming victims have been identified and more than 30 people arrested as part of a major investigation into potential organised crime.
The PSNI has launched a major investigation and called in experts from other parts of the UK - including those involved in the recent major investigation into organised child abuse in Rochdale.
Assistant chief constable George Hamilton said: “We see children who are taken to parties and who are offered drugs for free and then at some point have to pay that back through sexual acts.”
Most of the children involved lived in residential care homes at the time of incidents, but the allegations relate to periods when they were not in the facilities, such as on nights out when they failed to return.
Some suspected victims went missing 137 times from January 2011 to last summer, when a wide-ranging police investigation was launched, Mr Hamilton said.
Boys and girls have allegedly both been targeted.
Mr Hamilton added: “Many children are offered friendship, care, love and presents and accept drugs. Some are then threatened and it can be a progressive set of criminality.”
He told Stormont assembly members: “We have some evidence of children being put in a taxis and sent to another town for the purposes of attending a party or meeting other people.”
“That for us, that has the hallmarks of trafficking.”