Gunmen kidnapped 15 children on their way to school near Nigeria's oil-rich and troubled southern delta.
Police said they stopped the schoolbus as it headed toward the Abayi International School, took the mobile phones from the pupils, the driver and a teacher before taking the children away.
The kidnappers apparently demanded more than US$130,000 (€96,414) to release the children.
Abia state, in Nigeria's south-east, sits near the Niger Delta, a maze of mangroves and creeks where foreign oil firms draw crude in Africa's most populous nation.
The region has long been plagued by violence from militants upset about the region's unceasing poverty and from opportunistic criminal gangs targeting foreigners for kidnappings.
Now, with oil firms keeping their workers hidden behind razor wire and under paramilitary protection, gangs have increasingly turned to middle-class Nigerian families.
Last week, pirates operating off the delta's coast kidnapped three French oil workers and a Thai national. They have yet to be released.