That was a nice moment, I think, as we ride the escalators, and I notice my wife is squeezing my hand, warmly. Clearly, she is thinking what a wonderful father I will make, and all because I have the ability to pull funny faces at children.

As we walk down Upper Street, we stop outside a toyshop and look at the small wooden animals. There's another child in a buggy and this time, with no hesitation, I launch into my funny face routine. She's delighted, and claps her hands together, and her mother looks round, and sees me doing my funny face, and she looks delighted too.

This is amazing! I think. I'm some kind of joy-bringer!

We walk home, my wife clinging tightly to me, and when we get there she brings me a beer and lets me watch Gladiators.

There has been some kind of shift in the way children view me. Up until recently, they seemed to look at me with dark suspicion or disdain. Or I was an irrelevance to them, just a big, lolloping shape, shifting about nearby, scuttling around with a copy of Metro or an iPod. Nowadays, it seems, I'm some kind of potential friend. And all since I discovered the funny face. Does everyone know about the funny face? Why had no one told me about the funny face?

And then, a day or two later, I am sitting on the tube, heading for home, when I look up from my paper and see a small boy in a buggy, staring at me. He looks unsure of me, with big wide eyes and a concerned face. I turn my iPod off and smile at him, but he still just stares at me, as the carriage jolts around.

Poor thing, I think. All this noise. All these strangers.

I look at my paper again, because I'd just been reading a very interesting article about a fisherman whose feet went blue, when I remembered something: the funny face. The smiles and laughter I'd brought to London's children. The joy and warmth and delight in my wife's dancing eyes when she'd realised children now respond to me - that I was at that age. That they saw in me not a stranger, but a mentor, a father-figure ... a hero!

I put the paper down again and look at the boy. He starts to smile almost immediately. I smile back. This will be great. Has he seen the funny face before? I wonder whether to build up to it, or just launch straight in, and I start to remember when I was a kid, and a stranger had shown an interest, and I glance around the carriage and lock eyes with his mother and realise I've been staring at her child for a little too long.

Instinctively, I look away, and continue reading about the fisherman and his blue feet. But then I start to bristle.