Mom witnesses moment boy, 3, comforts terminally ill baby brother: 'Everything is OK'

A mother of two captured a heartwarming and heartbreaking moment between her sons, and is sharing it with the world.

Sheryl Blanksby found her 3-year-old son William comforting his infant brother, saying "everything is OK."

She snapped a photo and shared it on ?taken-by=mschikee">Instagram with this message:

#Throwback to when we were on our holiday. I was getting ready in the bathroom and husband was in the kitchen. The kids were quiet, especially Mr preschooler. You know the rules about when kids are quiet. I tiptoed to the lounge with my camera ready to catch anything they are doing. 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 #myheartandsoul #luckymummy

According to Fox News, Blanksby and her husband learned last month that their son Thomas had a malignant brain rhabdoid tumor. The boy was just 11 weeks old.

She blogged in December about Thomas being the family's "Rainbow Baby" -- a term often used to describe a child born after a miscarriage.

The irony of life has hit my family so hard and everything doesn’t make sense anymore,” Blanksby wrote on March 4. “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.”

The family doesn't know exactly how much time they'll have with baby Thomas.

“Watching my two sons together is a dream come true,” Blanksby wrote. “Being a family of four has always been part of my day dreams. It’s now my reality and it’s trapped in this nightmare no family should be in.”