Brisbane parents Krystal and Steven Edwards say they are trying to be strong but are consumed by grief after the unexpected death of their 23-month-old daughter Ruby who contracted COVID-19.

Mr Edwards said his daughter suddenly became unwell and eventually tested positive to COVID. She died on Sunday just two weeks before her second birthday.

He said when Ruby contracted COVID it triggered Acute Hemorrhagic Leukoencephalitis (AHLE), a very rare neurological condition that was caused by inflammation in Ruby's brain and spinal cord.

"This triggered a rare auto-immune condition, where her immune system, while trying to fight the virus, also attacked her brain, affecting her vital functions," Mr Edwards said in a social media post.

"Thanks to her treatment, we don't believe she suffered any pain during her fight and was able to leave this world peacefully."

The family are also preparing for the birth of their son in just two days.

"It feels like the world is falling apart for us right now, as we prepare for the arrival of our son ... this is supposed to be such a happy time where our family would become complete but is now so broken," Mr Edwards said.

"We are all hurting, we are all in pain, please be kind and be there for each other."

The family thanked the medical team at Logan Hospital and the Queensland Children's Hospital who "did their very best".

Mr Edwards told the ABC he did not want to "propagate fear but maybe caution and a reminder to cherish those you love because you just don't know when it can all be taken away from you".

"She was a gentle soul, loved her cuddles and was adored by all that were fortunate enough to meet her," he said.

"Ruby had the most beautiful long eye lashes, infectious smile and stunning hair colour.

"She was very clever and had so much potential. It's a shame her full potential will never be realised and the world has been deprived of such a special gift."