The Tamil Tigers have not confirmed or denied involvement, but have said they are to investigate the incident and punish any of their fighters found to be involved.
A spokesman from the Tamil Tigers said: "We are now making an inquiry into that matter. If it has been done by any of our cadres, our leadership will take stern action against them."
The abductions are thought to be part of forced recruitment drives, although the Tamil Tigers have in the past denied recruiting child soldiers.
Sri Lanka has seen a large number of abductions this year, which have been blamed both on the Tigers and on a splinter group led by a commander called Karuna.
Nordic truce monitors suspect Karuna is supported by some elements of the military.
Last week, in a separate incident, the vice-chancellor of Sri Lanka's main university was abducted in Colombo, the capital.
Civil war in Sir Lanka started in 1983, with the Tamil Tigers fighting for the independence of the minority Tamil community in the north and east of the country.
The war is estimated to have so far killed more than 67,000 people and displaced tens of thousands of people from their homes.