Kourtney Kardashian has shared a heart-warming post to celebrate her sons birthdays.

The 37-year-old 'Keeping Up With the Kardashian's star has described herself as the ''luckiest mommy in the world'' as she posted a picture of Mason and Reign, who celebrated their seventh and second birthday respectively, on Wednesday (14.12.16), on Instagram.

Alongside a photograph of her eldest and youngest children - who she has with her on/off partner Scott Disick, 33, the brunette beauty wrote: ''My twin boys born five years apart. Luckiest mommy in the world. Happy birthday to them. (sic).''

And the television personality gave Reign an extra birthday tribute, as she uploaded a picture of him standing on a bench sporting a tracksuit.

She captioned the post: ''Birthday boy (sic).''

Kourtney also took to Snapchat to showcase the surprises left around her house for the birthday boys, which saw her pan around her bathroom where 'Happy Birthday Mason' was scribbled on the bathroom mirror in red lipstick, with an elf hanging next to it.

Speaking in the video, the mother-of-three - who also has four-year-old daughter Penelope - said: ''The elf with the lipstick 'Happy birthday Mason'.''

To which Mason replied: ''Yeah it's my birthday.''

Kourtney later revealed her house was covered in glitter due to a visit from the fictional character, the tooth fairy.

She said: ''There's fairy dust everywhere, and the tooth fairy came. Two dollar bill.''

And the star showcased a variety of tasty treats for her children, which included a ginger bread house and mini cupcakes decorated with red icing for her sons, whilst a cluster of Mickey Mouse helium balloons were pictured hanging in the room on the site.

Kourtney's 61-year-old mother, Kris Jenner, has also paid tribute to her grandchildren on their special day, which saw her describe the pair as ''two sweet boys''.

Alongside a cute picture of the boys hugging one another, which she posted on her photo-sharing site, she wrote: ''Happy birthday to these two sweet boys!! Our precious angels Mason and Reign. I love you more than words can say. #myheart (sic).''