What is a fun childish thing you still do as an adult?
For me, it's sticking my hand out of the window of a moving car. Whether I'm driving or not, I love having the windows down and waving my hand in the wind. I've loved it since I was a child and I'll never stop doing it!
Sandwich biscuits (like Oreo and the likes, but there are plenty local brands) are extremely popular among kids where I live. I still eat them, the same way as I did as a kid: split them in halves, eat the filling-less halves, and then join the halves with filling so I get to eat biscuits with 2x more filling.
Oh thank god I'm no longer alone! Not that I probably was, I imagine tons of people do this, but I was the only one in my family that did. Whoo! There are at least two of us now!