His mum timed it: Just 21 seconds.

That was all it took for Wendy Atkinson's 2-year-old toddler Brodie to scale the pool fence at their family home, undo the latch and, grinning wildly, swing into the pool area on the open gate.

The first time she saw her son perform the feat, she read him the riot act.

But after a spate of drownings, Atkinson decided to film it to warn parents just how vigilant they need to be.

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"The fact my son is in a nappy really brings the issue home," Atkinson, a 38-year-old mother of four from Adelaide, Australia, said.

"It does start with supervision, but children - as quick as they are - can get out of your clutches. And when they do, 21 seconds is not enough time for any parent to react.

"The standard height of a pool fence is 1.2m and it's not high enough. Clearly no fence is safe, not one of them is a deterrent for some kids."

Atkinson also said Brodie tips out his "sippy" cup and uses it to stand on while winching himself up onto unreachable surfaces.

"If you innocently give your child a cup of water while outside, a taller four or five-year-old child can tip that drink out, stand on it and pull themselves straight over the top and they're gone," she said.

"Clearly there are a lot of issues with fences. Even lockable gates in an emergency situation hinder you from getting anywhere near that child in time.

"These are very serious and warranted issues. I wanted it to sink into peoples mind just how quick these kids are."

Atkinson said her heart was breaking for all the families who have lost their children.

"It's vigilance, but it's also just really hard," she said. "I've got three other kids to watch, and these poor families are being absolutely hammered - and for what? It's a never ending battle.

"I'm no expert, by any stretch of the imagination, but my son is teaching me and others that we need to pay attention. He's telling us that it is so easy."

New pool safety legislation for New Zealand came into effect on January 1 of this year. Key changes from the 1987 Fencing of Swimming Pools Act include spa pools and hot tubs not requiring fencing, and three-yearly inspections of swimming pools.