The head of Unicef warned that people may still be trying to smuggle children out of Haiti and said protecting youngsters who survived the earthquake is the top concern of the UN children's agency.
Ann Veneman said in an interview that Unicef is starting a programme to identify children who lost or can't find their parents.
The group is also working with other groups to put children who are alone into facilities where they can receive food, water and psychological help, she said.
"This is a children's emergency," she said.
Ms Veneman, who visited Haiti last week, said in every humanitarian crisis there's a risk that children will be trafficked out of the country for sexual exploitation, adoption, child labour or other illegal purposes.
In Haiti, she said, "this is a big concern".
Last week, 10 Americans were charged with kidnapping and criminal association for trying to take 33 children into the neighbouring Dominican Republic on January 29 without proper documentation.
The Baptist missionaries said they were heading to a Dominican orphanage following Haiti's devastating quake, and had only good intentions.
Ms Veneman said Unicef learned of some other instances "where there is concern that children may not have (had) the necessary documents when they left".
At the airport in Port-au-Prince and the border with the Dominican Republic, specially trained officials are now checking documents, which Ms Veneman said should make a difference.
Ms Veneman declined to comment on the detained Americans, saying the judicial system in Haiti is handling the case: "I think we need to await the outcome of those proceedings," she said.
Ms Veneman said Haitian Prime Minister Jean-Max Bellerive expressed concern at the massive media attention directed at the detained Americans.
"As the prime minister said to me in a meeting with him, 'I spend so much of my time answering questions about these 10 Americans when I have 2 million people in need here'," the Unicef chief said.
Even before the Americans were detained, fears that child traffickers would take advantage of the chaos following the quake led Mr Bellerive to announce that all foreign adoptions would need his personal approval.
Ms Veneman said there is no estimate of the number of children left alone as a result of the January 12 quake.
Before it struck, there were between 300,000 and 350,000 children in residential care facilities but many were left by parents too poor to take care of them, she said.
Ms Veneman said some care facilities and orphanages collapsed in the quake, killing children, though nobody has any figures.