The cousins that celebrate together, stay together! Kourtney Kardashian's son Reign Disick and Kim Kardashian's son Saint West had a joint birthday party earlier this December and the Keeping Up With the Kardashians stars have finally shared a few pics from the celebration. Saint, who just turned two years old on December 5, and Reign, who turned three on December 14, indulged in an adorable Monsters, Inc. theme.

"The kids had such a fun afternoon," Kim wrote on her website. "How cute were Saint and Reign's matching cakes? Sharing moments like this with cousins [is] the absolute best!"

Kim, 37 — who is also mom to daughter North West, 4, and has another baby girl on the way via surrogate — also revealed on her site that the kids' birthday party included some holiday-themed elements like an "elf-making craft station," an ice skating rink, and a visit from Santa and Mrs. Claus.

Kourtney's youngest with ex-boyfriend Scott Disick, Reign, ran around the whole party while dressed up as Sully from the Disney-Pixar movie.

"Since the monsters in the movie are blue, purple and green, we used those colors for all the decorations," Kourtney wrote on her website. "Obviously, running around with Mike and Sulley was the highlight of Reign’s day, LOL!"

"We had Santa and Mrs. Claus come and take photos with the kids — so we set up a few photo zones for families to pose together," the 38-year-old, who is also mom to Penelope and Mason Disick, continued. "I also put outdoor rugs and oversized pillows on the lawn in a few different places, so kids could hang out in the shade."

The mom of three also went on to reveal that the ice skating rink featured in the pictures was actually her basketball court, transformed for the party and the rest of the holiday season.

Kourtney also revealed that desserts included s'mores, gingerbread cookie sandwiches, and even a cupcake station for hungry tots. Adults had the choice of mocha or peppermint lattes a la the coffee station.