How to play like a child again?

I miss being a child.
You may ask: “Then just act like one again?”
Well I’ve tried.
I’ve got a great set of friends; we trust each other so we’re not afraid to act silly in front of each other. But we never start playing a game to actually enjoy it like a child.
And I know why.
It’s because we’ve forgotten how to play like children play.
So I ask you, wise community, to throw away that wisdom for two minutes, and dig inside your memory, and tell me how you had (or still have) fun like a child.
Maybe you have children yourself, then I ask you: How do they truly amuse themselves? What’s their favourite thing to do when playing?
If not, then what were your favourite things to do as a child to have fun?