Childish things

Ah, to be young again! The sense of wonderment and awe arising from the simplest of things!
At my age (north of 30...) sources of elation are few and far between.
Looking after my god-daughter and her brother, I was reminded of when I was but a lad, those many years ago. I distinctly remember the excitement created from something as simple as a large empty room.
What is it about large empty spaces that make children want to run around?
What other childhood pleasures fade as one becomes an adult?
Why must one "put away childish things"?

Bye for now - I'm off to buy some Lego.