Police found three children who had been trafficked to the UK and were living in squalid conditions when they raided a cannabis farm in Rochdale.
The youngsters were being "criminally exploited" to farm the cannabis plants at the address on Livsey Street.
It's believed they had been brought to the UK from Vietnam and were living with just three mattresses on the floor for them to sleep on.
Police say they had been unable to leave the premises in case they raised any suspicions.
The youngsters are now being supported by specially trained officers.
The cannabis farm had an estimated street value of £850,000.
No arrests have been made.
Philip Key, from GMP’s Rochdale district, said: “Tackling the exploitation of children is a priority for the police and we will do everything within our power to find those responsible and bring them into custody.
“Abusing vulnerable children for criminal gains is disgusting and our team is committed to dealing with this type of crime in all of its forms and making Rochdale – as well as Greater Manchester – a safer place.
“I want to ask that anybody with any information about this cannabis farm, or anybody who may be connected to it, to please contact us at the very earliest opportunity.”