Two children, aged five and six, have become the latest victims of kidnapping by gunmen in Nigeria's Delta region.
A security source said the two are the children of employees of the French energy group, Total, who were snatched on the way to school in Port Harcourt.
Young children have become the targets for militants in the oil-rich Niger Delta region in recent months.
Seven oil workers, including three foreigners, who were seized from an oil rig on Sunday, were freed on Monday.
The seven, including four Nigerians, a Croat, a Russian and a Briton were unharmed and in the custody of the Rivers State government, a state official said.
They were abducted on Sunday by gunmen in boats from an oil platform belonging to Royal Dutch Shell.
Militant groups are calling for a greater share of Nigeria's oil revenue to be spent in the Delta where it is produced.
The main militant group in the region, the Movement for the Emancipation of the Niger Delta (Mend), called off a truce with the Nigerian government a month ago.
The unrest has caused a drop of more than 20% in oil exports from the Delta in the past 18 months.