Sheryl Blanksby, from Western Australia, gave birth to a little boy named Thomas just over three months ago.
When Thomas was born doctors noticed a small lesion on his right arm. When he was six weeks old doctors found a lump on the left of his abdomen, which ultrasound tests showed was a tumour over a kidney.
Thomas was diagnosed with malignant rhabdoid tumour, a rare and aggressive form of cancer most common in children. Doctors then found multiple tumours in both of Thomas' lungs. The cancer had spread, and doctors could not give Sheryl and her husband Jon a time frame on how long Thomas had left to live.
"The irony of life has hit my family so hard and everything doesn't make sense anymore," Sheryl wrote on her blog. "It feels like only yesterday when I posted about giving birth to our rainbow baby Thomas and here I am writing about his imminent death.
"I can't even begin to describe the pain I feel each time I look at his precious face. My heart breaks for every big smile he gives me because I know how much I will miss it when it's all gone, and when you think my heart can't take it anymore, it shatters even more when he gives his begging look when he's in pain."
Last Wednesday Sheryl shared a photo her other son, three-year-old William, comforting his little brother Thomas.
"I was expecting my baby to be covered in Nutella or something but instead I saw this," wrote Sheryl. "My preschooler is telling his baby brother 'Kuya (big brother) is here. Everything is ok'."
Sheryl's touching photo picked up thousands of likes and prompted a fundraising effort set up by the Blanksby family's friends.
In a matter of days the fundraiser raised $42,000, more than twice the original goal. The money will go towards making sure the Blanksby family can do everything they want with Thomas.
"Our family still can't believe the love we've been receiving from people all around the world," Sheryl told BuzzFeed News.
"One of the reasons I started sharing my son's journey was to get prayers from family and friends and the idea that the 'whole world' is praying for my son is just beyond amazing."
Sheryl says that the whole family is "gobsmacked" with the fundraising effort, and hopes to go to the beach, have picnics and play dates, and organise ways to make keepsakes of their time with Thomas. Recently, the family went to a water park and also made foot and hand moulds of young Thomas. A road trip is also planned.