A mother-of-two has offered a selfless gift to her dying best friend – legally adopting her children.

Missy Armstrong from Illinois made the decision after Sara Hankins was diagnosed with a fatal neurological disease.

Ms Armstrong, her friend of nearly 20 years, is now in the process of legally adopting three of Ms Hankins’s four children, aged eight, nine and 11. She will also take in the fourth child, who is 18.

“I thought, yeah, I can do this. I love them, and I’ve known them their whole lives. I make a decent living. I have the support of her family,” Ms Armstrong told NBC’s Today show.

The pair became best friends after meeting during training to become hairdressers in 1999.

“She would grab her kids and come to my house, or I would grab my kids and go to her house. We were always together,” Ms Armstrong said.

Ms Hankins was diagnosed last year with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease and motor neurone disease.

Her biggest fear was what would happen to her children after she passed away.

Sara Hankins was diagnosed with a fatal neurological disorder (Facebook)

Ms Hankins is now being cared for at her mother’s home.

She told of her shock at Ms Armstrong’s generous offer.

“I couldn’t stop crying. My number one concern was keeping my kids together, because I think what they’re going to go through is hard enough,” she told Today.