Oh my gosh, they are so cute!

To celebrate her niece Penelope Disick's fourth birthday on July 8, Kim Kardashian posted an oh-so-adorable Instagram video of her own daughter North West, playing with the birthday girl, along with a special bday message -- and it's next-level adorbs!

Along with the sweet video of the tiny tots, the svelte 35-year-old wrote, "Whatever secret language u girls speak, the way you girls protect each other & love each other is so special."

The proud aunt added, "Penelope, North is so lucky to have a best friend like you! Happy Birthday my sweet P. I love you to the moon and back!"

The video shows Penelope, who is Kourtney Kardashian's middle child, grabbing her younger cousin Nori's arms and swinging them about as they sing gibberish together. We're a little worried the twosome are going to topple over — but we guess that's part of being a kiddo!

In the clip, Penelope is wearing a gray tank top and black pants, while her three-year-old cousin is dressed just like a little Kardashian, outfitted in a white tank and cut offs.

North, who turned three on June 15, had a point birthday party with Penelope in late June -- and it looked pretty rad if you ask us!

Kim took to Kimkardashianwest.com to post photos of the Little Mermaid themed bash. Kanye West's lady love also wrote, North and P had a joint mermaid party over the weekend! They are obsessed with mermaids, so we gave the party a fun 'Under the Sea' theme."

A wigged-out Khloe Kardashian posted an adorable snap from the event with the caption, "The best seat in the house with my Mermaids and my Mase."

UMM WE WANT AN UNDER THE SEA BIRTHDAY PARTY AND HAVE TAIL SKIRTS!

The best seat in the house with my Mermaids and my Mase

A photo posted by Khloé (@khloekardashian) on