VIDEO: This little girl really doesn't want her baby brother to grow up

When Sadie realises that her baby brother isn't going to stay small and cute forever, she has a bit of an existential crisis.

We've all been there - that crashing realisation that life is fundamentally unfair, that everyone has to grow old and die and there's nothing you can do to change that.

And she's only five years old.

What really makes this video is the calm, benevolent smile of her adorable brother who has absolutely no idea what all the fuss is about.