Namakkal District Superintendent of Police P Kannamma said they raided the house at Janam Elampillai, 35 km from here, after an adjacent house belonging to the family was damaged when some gelatine sticks stored there exploded last night, injuring a four-year-old boy.
Ramalingam, a fisherman, and his wife Sarasuvathy used to catch fish in the Cauvery river and had stocked the explosives for using them for trapping the fish, police said.
Last night, ten gelatine sticks and an equal number of detonators kept in the kitchen of their adjacent house exploded, injuring Sarasuvathy's grandson.
The arrested included Sarasuvathy's in-laws and the seller of the explosives.
The five, arrested under the Explosives Act, have been remanded in judicial custody and lodged in the Salem central prison, police said.