A mother has released a warning to fellow parents after her three-year-old son opened a pool gate by himself and let his little sister inside.  

Krystal Hill, from Perth, filmed Isaiah climb onto the roof of a red and yellow toy car parked by the pool gate in the family's backyard.

The savvy three-year-old successfully stretched himself to the top of the fence, where he was able to unlock the mechanism. 

Isaiah's toddler sister entered the pool area and he followed, before shutting the gate behind the pair.

'So you think pool fences are safe!' Ms Hill wrote on Facebook with the heart-stopping footage.

'I watched my three-year-old who can't swim independently yet, climb up and open the pool gate and then let himself and his little sister into the pool area.

'I am in a bit of shock at the moment!'

The savvy and well-balanced three-year-old successfully stretched himself to the top of the fence, where he was able to unlock the mechanism

Isaiah's toddler sister entered the pool area and he followed, before shutting the gate behind the pair

Ms Hill's video has 1.7million views and has been shared more than 42,000 times.

She said a number of fellow parents have sent her messages to thank her for sharing the video and raising awareness.