'When you want something so much and really love it, you almost don't want it at all'

"How many days?" Jacob asks, pulling on his dressing-gown and slipper socks, peering at his Flora and Fauna of Australia Calendar and shuffling a pile of Animals of Farthing Wood stickers which he keeps by his bed.

Outside it's black, freezing, lifeless - a criss-cross of dark branches and dim lights shining from the flats at the back. I yawn, shiver. "Just one. It's tomorrow."

Jacob sighs happily. He knows this already, just wanted me to say it. "It's my Birthday Eve."

We go to wake Chloe (Raphael's been awake for ages, whispering into my ear about castles and beasts). She's on the top bunk, thumb-sucking. "Go way!"

I talk her down the ladder, one rung at a time.

Downstairs, I allocate Weetabix and Raisin Wheats, pour food into cat bowls, make Jacob's packed lunch. I slice some banana into Raphael's bowl. "Don't give me black bits! Cut off the black bits!"

"You know, I'd really rather not go to judo on my birthday," says Jacob airily, already spoilt in anticipation of all those treats. "Just think, I get no time at home at all. When am I going to manage to play with everything?"

"There are plenty of days," I say. "You ought to go. See what Daddy thinks."

"Daddy says see what you think."

"Well then, we'll see." I mash eggs in a bowl, fill a brown roll, grab apple, yoghurt, plastic spoon, Muesli Bar, put them into the Stingray lunchbox.

"Not a Muesli bar!" Jacob groans, watching me. "Not on my Birthday Eve!"

"If you don't eat this, then you're going back on hot lunches." I snap the lunchbox shut.

"But Mummy, you should see what other people have. I'm the only one who doesn't have some sort of a treat in their lunch box - something chocolatey or a drink or something. Frank and Jamie do every single day!"

"Jacob, when you're an old man and you're healthy and you have all your teeth, you'll thank me. You'll come and visit me and you'll say, 'Beautiful, sensible Mummy, I love you, thank you!' "

"Yeah, yeah."

"And Frank and Jamie will be taking their teeth out at night and putting them in a glass by their bed."

"In a glass slipper?" asks Chloe, Weetabix halfway to her mouth.

"In a glass of water. They'll have pretend ones which they have to take out, because they'll have lost all their real teeth because they had sweets in their lunch boxes."

"But. But. But," says Raphael, with his urgent, three-year-old need to speak before he's decided what to say. "But I want to lose all my teeth and then the Tooth Fairy will come and then - and then - and give me lots of money and I can go to Peter Jones and get some more Batman toys."

"No," says Jacob, who still - mysteriously - has every single one of his baby teeth and is somewhat aggrieved. "These are different teeth. It's good to lose your first teeth, it's bad to lose your second teeth."

"Or you don't lose your teeth," observes Chloe, holding her hand out, palm up. "But they all turn black and silver like Mummy's."

"My actual teeth aren't black," I protest quickly. "But I have millions of fillings."

"Mummy ate lots of sweets." This triumphant, jealous.

It's true. After dancing class, we all sat in a row on the cold stone steps of the YWCA and held out two hands and Smarties were dropped into them by the teacher with her straight back and stiff skirt and shoes with the button straps. "Chins up, tummies tucked in."

We held out our skirts and pointed our toes and were rewarded with sugar - poisonous sweetness for sweet, obedient little girls - rotting cavities stopped up with amalgam. I liked orange Smarties best. I remember the coloured sugar shell which you sucked till it was pale blue then frail white and then it collapsed to let the chocolate melt through, and just thinking of this brings back the stony chill on my five-year-old bottom and the meaty-leather smell of ballet shoes.

"Anyway," I tell Jacob, "you've got a special lunch for your birthday tomorrow, with lots of treats."

"You're the best mummy in the world," he beams greedily. He eats his porridge thoughtfully. "You know, in a funny way, part of me doesn't really want my birthday to come, I wonder why that is."

"You don't want it to be over?"

"It's just that when you want something so much and really love it with all your heart, you almost don't want it at all," he pauses. "Do you know what I mean?"

I stand, transfixed by this glimpse of his soul. He is unique, a separate heart and mind. He's nearly seven. "I know exactly what you mean," I say. "You said it very well."

Upstairs, Jonathan's getting out of the bath. "This time seven years ago, we had no children," I tell him. "We could come and go as we pleased, drink, stay out late, go to the cinema on impulse."

"We could start work at four-thirty in the afternoon if we wanted to," he says wistfully. "Go on till midnight."

"And have no food in the fridge and not wash any clothes for a week and be ill whenever we wanted."

"Why did we do it?" he asks me. "What were we thinking of?"

"We were fertility-crazed."

"What did we do all the time?" he asks, drying himself, looking out of the window where granules of snow are skittering across the frozen pavement in the wind, Siberia-style.

"We sat around," I say. "It was wonderful."