Sibling love is a thing of profound beauty, and this struggling mother of two got to experience firsthand its overwhelming joy when she witnessed a heartwarming moment between her two sons.

After a recent family vacation, Sheryl Blanksby took to Instagram to share with her friends the highlight of her holiday: a photo of her 3-year-old toddler comforting his baby brother, who has been diagnosed with an aggressive and lethal form of cancer.

A Moving Message

Sheryl wrote in her Instagram post that the house was suspiciously quiet that day and so she naturally assumed the boys were doing something they weren't supposed to.

Since she expected to find them making a mess and wanted to create a funny family memory out of her children's exploits, Sheryl tiptoed in the room, camera in hand, looking to surprise the little "troublemakers."

Instead, the surprise was on her as she discovered the toddler beside his baby brother, whispering words of comfort: "Big brother's here. Everything is OK."

This little boy's moving message has a lot to teach us about compassion and empathy, and above all family loyalty.

Sheryl captured the sweet, candid moment on camera and later posted the precious holiday keepsake on Instagram.

"I was expecting my baby to be covered in Nutella or something but instead I saw this. My preschooler is telling his baby brother 'Kuya (big brother) is here. Everything is OK.' #myboys #bestbigbrother #documentinglittlemoments #mybabyloves #heartandsoul #luckymummy," she captioned the photo.

A Rare And Unforgiving Condition

Sheryl's family received a hard blow when her youngest son was diagnosed with cancer at only 11 weeks. The baby, now 14 weeks old, suffers from a form of kidney cancer called malignant rhabdoid tumor (MRT), a rare fatal condition that mostly affects infants and toddlers.

The cruel diagnostic devastated the family, who just three months earlier were rejoicing at the birth of baby Thomas, a "Rainbow Baby" born after a miscarriage.

The mother uses her blog as an emotional outlet to write about her painful experience, and her posts are beginning to raise awareness about this uncommon disease.

Family friends set up a GoFundMe page relating in detail Thomas' MRT diagnostic and the ordeal of undergoing a nephrectomy - kidney removal surgery - before doctors determined his tumor was incurable.

Malignant rhabdoid tumor affects 20 to 25 children every year in the United States and is usually discovered at an average age of 15 months. This form of cancer typically starts in the kidney, but can appear in other organs, including the brain, and has been shown to metastasize.

The causes of this type of tumor are still unclear, but researchers have isolated the SMARCB1 gene, which exhibited mutations in nearly all encountered cases.

Extremely aggressive and difficult to treat, this condition leaves children vulnerable to developing second tumors, especially if the SMARCB1 gene begins mutating in healthy cells.