River Arama Parry died at a relative's home in Fisher on Wednesday evening.

The 21-month-old toddler and his family were visiting relatives in Canberra from Perth when the tragedy occurred.

Paramedics rushed him to Canberra Hospital but he could not be revived.

His grieving mum, Tynan Abel, said he was "the light of everyone's life".

"Having him was like breathing for me. He was my laughter, he was my pride and joy, he was my best friend, he was my little shadow. Wherever he went there was no darkness, just light."

Cheeky, curious and mulishly stubborn, River was adored by his two dads, biological father Sam Parry and step-father AJ Abel, and his three sprawling families, his mum said.

He loved rugby and basketball – "the way we'd usually put him to sleep is we'd put the LA Lakers on YouTube and he watches it," Mrs Abel said – and wrestling with his big, burly uncles.

His laugh, which bubbled out at every little thing, was infectious and he loved to sing songs from the film Frozen.

"I didn't think that he would get on that bandwagon [but] he'd point to a computer or a phone or a tablet and say 'Mum, Let It Go!'. He ended up changing it to 'Let It Go' to 'Go Away' so he started singing 'Go away, Go away!'"

But River was also a sweet soul, brimming with love for everyone he knew.

At his mother and step-father's wedding last month, he made a game of collecting kisses from the pair of them before squashing their faces together for a smooch of their own.

"He brought me a lot of joy. My son gave a lot of love and touched a lot of lives. Since he was born he's always been there for me to touch my hand to tell me everything is going to be alright. Even now, I feel him touching my hand to say 'Everything is going to be all right mum'."

His step-uncle, Brumbies player Robbie Abel, said River was the happiest boy he'd ever known.

"He acts like every day is the best day of his life, which is a pretty good example to me. He's a little kid that brightens everyone's day, that's the kind of kid he is," Mr Abel said.

"He's always happy, always cheerful, he's one of those kids that's very easy to love. It's like that because he finds it so easy to love you."

Mrs Abel pleaded with other mums and dads to never take their little ones for granted.

"Play with them if they're pulling on your shirt and you're washing the dishes and they just want a moment of your time. Play with them because that time means everything to them. That moment means everything to a little boy or a girl," she said.

A GoFundMe page set up by friends of the family to help support his parents and pay for his funeral raised close to $9000 in just seven hours on Thursday.

Police are investigating the circumstances around River's death but a spokeswoman said it was not believed to be suspicious.

Part of that investigation will include examining how the pool was fenced, she said, and a brief will be prepared for the Coroner.

People can make donations at www.gofundme.com/78gxfub8