Mother Julie Tattam wrote about the “super scary” ordeal on Facebook as a warning to other beachgoers.
Ms Tattam was snorkelling at Salmon Haul Beach in Cronulla, in Sydney’s south, on Wednesday when her daughter bounded out of the water with a shell in her hands.
“Look at this gorgeous octopus, I caught it in this shell,” the 11-year-old told her mother.
Upon closer inspection, Ms Tattam discovered her daughter was holding a blue-ringed octopus.
“She walked all the way up the beach to show us and the octopus started crawling out of the shell towards her hand so she dropped it onto the rocks,” the mother said on Facebook.
“I ran down to look and it was a blue-ringed octopus! She had been carrying it in her hands (luckily with the shell to protect her).
“I was so worried (in fact I am still shaking with ‘what ifs’) so I Googled them.”
The mother discovered blue-ringed octopi are deadly and a sting can send a child unconscious in minutes and cause their lungs to become paralysed.
“Death can happen within 20 minutes,” the mother said.
“We were a good 15 minutes walk from the car and then about 15 to 20 minutes drive from the hospital. So scary!”
Ms Tattam shared a photo of the octopus and warned parents to tell their children not to touch them.
“I didn’t realise they were so little – they are tiny like only five to seven centimetres long, and we had never thought to show the kids a photo of one.”
Ms Tattam said the octopus was not injured and crawled away into a rock pool.
The mother is also warning people not to be fooled by the colour of the octopus.
“Because it was frightened it went really blue,” she told Yahoo News.
“They are just pastel blue and mostly just look brown. They are not that bright colour all the time so don’t touch any octopus.”
Many commented on Ms Tattam’s post, thanking her for warning them about the deadly creature.
“OMG how terrifying for you,” one said.
“Thank goodness it didn’t harm her. My boys would have done the same thing as your daughter.”
According to Museums Victoria, the blue-ringed octopus is one of the ocean’s most venomous creatures.
Mitchell Ogg, 28, was pulled up a cray pot while on a boat near Garden Island when he felt the bite of the deadly creature.