A COCKBURN surf club has issued a sobering warning after a child allegedly brought home a deadly blue-ringed octopus inside a seashell.

Coogee Beach WA Surf Life Saving Club said the child was in front of the club collecting seashells and building sandcastles on Sunday.

The child brought the seashells home from the beach with the venomous stowaway inside.

Luckily, it was their aunt who was cleaning the shells and not the child when the octopus emerged.