The UN children's agency, Unicef, has begun registering thousands of tsunami orphans in Aceh in a bid to protect them from human traffickers.
There are fears that orphans could be vulnerable to criminal gangs
Unicef spokesman John Budd said one registration centre in Banda Aceh was already in operation.
There have been fears that human traffickers have started targeting the orphaned survivors of the tsunami.
Thai police said a possible case, of a Swedish boy missing in Phuket, did not appear to have been abducted.
Police said the boy, Kristian Walker, was never registered in the hospital he was supposedly taken from.
Mr Budd said one registration centre for orphans in Aceh was set up on Tuesday and several others would be in operation throughout the province by the end of next week.
He said that this was necessary because children remained extremely vulnerable.
"It increases enormously their never being reunited with their family and their vulnerability to exploitation in some way," he told the BBC News website.
Mr Budd said there had already been two cases of children being smuggled out of Aceh in recent days.
He said that in both cases, their abductors had been arrested and the children rescued.
Mr Budd also said there were unconfirmed reports of up to 20 other children being taken to Malaysia, and possible hundreds to Jakarta. And he has recently become aware of an SMS message being sent widely around Asia advertising 300 Aceh orphans for sale.
The Indonesian government has already banned children from leaving Aceh without their parents in an attempt to guard against child traffickers.
Jakarta estimates that some 35,000 children have been orphaned as a result of the 26 December tsunami.