The incident happened in Danzanke village – a remote community in the northwest Sokoto state.
The state’s health commissioner, Ali Inname, told journalists that the family mistakenly used fertiliser chemical that looked like salt in preparing a meal on Monday.
He said medical personnel tried to save the victims’ lives without success.
But two members of the family who only tasted the food are now receiving treatment in a hospital.
Following the incident, officials have once again advised people to always keep poisonous chemical substances away from their food stores for safety reasons.
Similar incidents involving families have happened in the past in Nigeria but the number of those who died in the latest case is unusually high.
Source: BBC