Mason Disick turns 5-years-old on December 14th and Kourtney Kardashian is making sure he's celebrating well in advance.

The reality star threw a "Nightmare Before Christmas" inspired shindig for her son and the whole Kardashian clan attended, including Khloe Kardashian, who Kourtney had dress up in a decked out costume while the rest of the party wore their regular clothes.

"Kourtney pulled a ‘mean girl' move on me and had me dress like Sally from The Nightmare Before Christmas while everyone else was mad chill," she said on Instagram. "lol thanks @kourtneykardash #MasonsBirthdayBash"