Thanks to one adorably over-the-top mermaid birthday party — and the ever-present Keeping Up With The Kardashians camera crew, of course — we already know that two of reality television's most adorable offspring, North West and Penelope Disick , are best friends. The kind of best friends who dominate Disneyland and do frighteningly funny impressions of aunts Kylie and Kendall , that is.But now, thanks to one amazing Instagram video, we know that the daughters of sisters Kim Kardashian West and Kourtney Kardashian are also the kind of best friends that share a super-cute secret language. (Second-generation #friendshipgoals?)In the video, Little P and young Nori stand on chairs and hold hands; smiling, laughing, and talking emphatically to each other — with not a decipherable English word uttered between them. But that doesn't appear to stop the clearly delighted dancing toddlers from communicating.“Whatever secret language u girls speak, the way you girls protect each other & love each other is so special,” Kardashian West captioned the video, which she posted in honor of Penelope's fourth birthday. "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!"We should all have friends who understand us so well.