Harriet Walker: How hard could it be to look after a baby?

I spent the first half of this summer only too pleased at the clouds, downpours and lingering chill in the air. I wanted the skies to reflect my mood, and if I wasn't feeling sunny or blithe, I was damned if anyone else should be.

But my spirits have risen with the mercury. As it has got warmer, I have come back to life under the sun's gaze, from dining al fresco to singing in the street in the small hours. As it has heated up, the surface area of my clothes has been inversely proportional to how sociable I have been feeling, and I have made fair-weather friends that I know will last me into winter, too. So I have been glad of this summer, after all.

Until, that is, two weekends ago, when things just got silly: 31 degrees in an urban heat island? I ask you.

I sat at an outside bar on the Friday night, my jeans sticking to me and my make-up evaporating, watching a man in his pants jump from the roof of his houseboat into the canal. The first time he did it, everyone cheered at his joie de vivre. The second, third and fourth times, we were a bit more British about it and shouted at him to stop being such a poser. The fifth attempt warranted gestures so obscene that I couldn't possibly set them down in print.

As I finished a frozen margarita and turned to the prosecco (drinking like this in warm weather invariably makes you feel like carrion the next day, so watch out), I got a message from my friend.

A brilliant opera singer, the after-effects of whose wedding I will be sleeping off by the time you read this, she had a rehearsal that clashed with her life as a mother, and needed help with childcare. So I said I would look after her baby the following afternoon. I said I would because I knew it was the right thing to do, and that it would help her out of a tight spot. I said I would because I was a bit drunk and I thought it would be easy.

Had I been less drunk, I would have remembered that I am not very good with children. Some of them, I really like. Others, I loathe. Some of them actually make my skin crawl. Most of them, I have no idea how to relate to and end up conversing with them as if they were miniature adults, like so many early modern woodcuts of the baby Jesus, in which he just looks like a shrunken 40-year-old. Every so often, a child will look at me with such boredom and disdain – or start crying so ferociously – that everyone in the room, me included, begins to wonder whether I'm actually a paedophile.

But I'd met this one before and read him a story, and he looked at me with such intense need and gratitude then that I had decided he was pretty great. So I said I'd look after him for an afternoon. How hard could it be?

The thing is, I hadn't banked on the summer having kicked off in earnest and the effect of heat exhaustion on my frail constitution. I am a delicate flower, me, all grey-skinned and translucent with an unfixable glitch in my homeostasis and the radiator behind my face which means I am always just a bit too hot. While everyone else looks impossibly cheerful and vibrant in the park, I am more often found draped in front of the TV, curtains shut, wearing my pants and chewing an ice cube.

When I met my friend and her son in Hyde Park, she was bound for the Proms, I for the pram. "He just likes to wander really," she said of the adorably squashy-faced Albie, "so don't worry too much about having to entertain him." Music to my ears: I planned to lie on the grass in the shade next to some Highland dancers upon whom Albert soon became transfixed.

But no, after five minutes, Albie wanted his sandwiches. Except he didn't want his sandwiches – which he threw on to the ground like a Medici flinging down a poisoned chalice – he wanted the clicky Tupperware box they lived in. Which he clicked and clicked and clicked. No problem.

Soon, he wanted to push his pushchair around, a fact I only realised when he became increasingly frustrated about the brakes being on and started barking at me. "There we go," I said, easing them off and watching horrified as he sent it rolling away down a hill.

But, by that time I had already strong-armed him into his buggy and marched him to a restaurant, plied him with shortbread and another friend had accidentally spilt beer on him (just a little bit), so Albert and I were firm friends; united simply by the fact of both being hot and a bit bothered.

This summer is nice and all, but I'm ready to put my coat back on again.