The children, ranging from 4 years to 15 years old, were found with a 44-year-old woman claiming to be a nun in the southern state in Nigeria's Delta region.
Police arrested the woman, Maureen Wechinwu, and said they were working to reunite the children with their parents.
"Investigation is ongoing with the view of arresting other suspects linked in the case," Eboka Friday, Rivers state commissioner of police said in the statement.
One rescued nine-year-old boy had been taken from a market in October 2020 in neighboring Bayelsa state and had already been sold to a woman in Lagos and returned to Wechinwu, police said.
Human trafficking is common in Nigeria, according to the U.S. State Department and non-profit organization Pathfinders Justice Initiative, with children kidnapped or coerced into domestic labor, sex work or other forced labor.