Travel blogger couple puts five-year-old son in shark cage

It's these holes -- gaps between the cage bars -- that have caused a minor internet storm.

Some Youtube commenters were quick to show their disapproval.

"Only takes a second and something can go horribly wrong with holes in a cage like that," one commenter said.

"I would never bring my small children into a great white shark cage!"

Since being uploaded in November, the video has clocked up more than 4.1 million views.

For Deborah Dickson-Smith, an Australian travel writer and director of Diveplanit Travel, it's irresponsible to take young children out diving.

"I think learning to dive with your kids is one of the most magical, bonding experiences you can ever have as a parent.

"But dipping your kids into a shark dive - before they are even old enough for the youngest level of dive training - is just mind-boggling."

In Australia, children must be 12 to scuba dive, though eight-year-olds are allowed to learn in other parts of the world.

While Manilla and Dorothy aren't actually scuba diving - which would involve a portable air supply - they appear to have some difficulties with their breathing equipment in the video.

"[Manilla] can barely fit the regulator in his mouth," Ms Dickinson-Smith observed.

"It's a really strange way to introduce your kids to diving and underwater."

But Andrew Fox, who operates Rodney Fox Shark Expeditions in Port Lincoln, South Australia, had more concerns about the sharks in the video.

Sharks can swim into poorly-designed cages, get trapped and die. That's exactly what happened at Nautilus Dive Adventures - the same dive operator used by the Bucket List Family. Just weeks after the family filmed their video, a great white reportedly died after getting trapped in a cage.

"The reason why that shark got captured in the cage is that the design of the cage had a lot of vertical bars," Mr Fox said.

"The sharks aren't actually looking to get in and bite people. Sometimes they just swim in and get trapped."

Mr Fox said Shark dives in Australia use equipment that's safer for sharks and divers.

"We tend to have a lot fewer gaps in different places. And we use a lot of mesh," Mr Fox says.

But whether in Australia or Mexico, shark diving is low-risk.

"There's never been a fatality in the history of shark cage diving," Mr Fox says.

Mr Fox lets children as young as eight on to his dives. He said he has occasionally taken out five-year-olds, but they have used a snorkel, not a hooker line.

Garrett Gee sold a mobile app he developed to Snapchat for $US54 million, according to Forbes. The couple started travelling in 2015 on a six-month trip which turned into years of travel and millions of followers on social media.

See also: Seven animal experiences tourists should never do

See also: Cape Town's great white sharks have disappeared and no one knows why