OMG! This is just TOO cute!

Penelope Disick celebrated her fourth birthday over the weekend with mom Kourtney Kardashian in the Bahamas, but she was definitely on auntie Kim Kardashian's mind. Kim Instagrammed the video above of Penelope playing with North, and while we're not sure what the girls are saying (or singing!), but it's absolutely adorable.

“Whatever secret language u girls speak, the way you girls protect each other & love each other is so special,” Kim captioned the clip. “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!”

Kourtney posted her own clips and photos on social media and added, “Happy birthday to my little mermaid! Seeing the magic in the world through your eyes makes me so happy." Aww!