Sheryl Blanksby shared a black and white photo which shows the young family snuggled together, and addressed her youngest son directly in the caption.
'Dear #littlewarriorthomas,' she wrote. 'Your #superkuyawilliam was looking for you everywhere in the house today. He thought we were hiding you to surprise him.'
'I told him you're in heaven now and he got worried that you will miss him so much. He was also worried that you will get wet from the rain.'
Dear #littlewarriorthomas Your #superkuyawilliam was looking for you everywhere in the house today. He thought we were hiding you to surprise him. I told him you're in heaven now and he got worried that you will miss him so much. He was also worried that you will get wet from the rain. I told him to look up the sky and say hi to you and to watch out for signs when you say hello back. We miss you so much darling boy. Love you always your mummy, daddy and Kuya. #documentinglittlemoments #wemissyou #thisisgrief #fuckcancer #fuckyoucancer
Sheryl approaches the difficult topic as delicately as possible, saying: 'I told him to look up the sky and say hi to you and to watch out for signs when you say hello back.'
Just one day before the touching post was shared, the grieving family announced on Instagram that their youngest son Thomas had passed away, following months battling a malignant rhabdoid tumour.
Sheryl, from Perth, Australia, has used her Instagram to document the difficulties she and her husband faced in the wake of Thomas's diagnosis, captioning each post with the hashtag #littlewarriorthomas.
The pictures posted of the little one show him as a healthy, happy baby boy, but he was suffering a rhaboid tumour in his abdomen, a rare childhood tumour that commonly starts in the kidneys but also can occur in other soft tissues or in the brain. The survival rate is just 30%, and treatment has not been known to be effective.
In the simple Instagram post confirming his passing, Sheryl wrote: 'It is with immense sadness that we share, our #littlewarriorthomas grew his angel wings yesterday night, 8th of May 2017 at 730pm. He was surrounded by family and right next to his mummy and daddy when he passed away. He fought the good fight especially when he was only expected to live for only short amount of weeks after his diagnosis.'
'His baby sibling who we miscarried before him that had the same due date was also taken away from us the same date 2 years ago and they are now together with our loved ones who are looking down upon us. He's no longer in pain is our only consolation.'
'We miss him so much everything hurts. Thank for all your kindness and support the last few months.'
Followers who had been swept up in the tragic story rushed to comfort the bereaved family and offer words of support. A GoFundMe page, that was set up to help the family make great memories during Thomas's short life, is still up and running in his name.
'Im so sorry for your loss. I cant even imagine the pain. I will pray for you. 💔,' one commented, whilst another added: 'Tears in my eyes as I read this. Your baby boy will be so missed. I wish you a lot of strength to deal with this loss as a family.'
'I am so sorry to read this news,' a third agreed. 'You gave that little baby such a beautiful time here in earth, full of so much love. My heart breaks for you all ❤️❤️❤️'