Could be very simple, this one – 5 kids, 5 things.  In fact I do refer to them as Things, straight from Dr Seuss’s Cat in the Hat.  Things 1 through 5 can be as destructive a force as they are in that book but they can also be simply wonderful.

1. You’re always learning – or re-learning stuff.  How does this work?  What does this do?  Why does that do that when I push this?  Questions I know for a fact I used to know the answers to!  I find myself racking my brains, surreptitiously consulting Google on my phone, asking around.  I used to know this stuff!  And, thanks to the kids, I’m re-learning it all again.  Thing 1 will be off to High School after the summer, so expect a whole lot more learning once she starts on the more advanced aspects of maths, chemistry…
2. Their boundless energy.  Kids are brilliant!  If we didn’t slow down as adults we’d all be like Jedward.  My kids run around, bounce off things, crash into things, cycle, run, swing, jump – and then they’re asleep before you’ve finished the bedtime story.  Life should be like this!  Do everything to the absolute max and then sleep the sleep of the justly sodding knackered.
3. Imagination.  It’s truly amazing what kids think up.  Give them five minutes in the garden and they’ll be playing something that they all somehow know the rules to.  Brilliant.  They don’t need dice, rules, cards, tokens, anything.  Oh, and if they see something they like on TV, then that becomes the game instantly.  The Things have only relatively recently discovered Ben 10, so that’s the game of choice right now.  Of course, they all want to be Ben, but that’s another problem.
4. Encyclopaedic Knowledge of Stuff.  I pride myself on knowing a shedload of stuff.  Almost none of it is of any practical use on a day-to-day basis but I was able to win £50,000 on a TV quiz thanks to being able to name more than half of the movies on the American Film Institute’s Top 100 Science Fiction Movies.  Or I would have done had I not been on the sofa shouting at the TV.  Kids soak up knowledge like a really big sponge.  Within a few minutes of watching the aforementioned Ben 10, they knew the names and powers of each and every alien he could change into, what the transformation animations looked like and who would be best to use in a situation like, say, going to school or avoiding homework.  Amazing.
5. Recognising Myself.  This is one of the true joys of fatherhood – parenthood in general.  Watching your child do something, consciously or unconsciously, and doing it in exactly the same way you do.  Really simple things like holding a pen, walking into a room, leaning back in their chair when they’ve finished their meal.