E Jane Dickson: 'Were we born cuddling a snake?'

We are at the Science Museum, peering at obscure and obsolete medical instruments in the Wellcome Wing.

We are at the Science Museum, peering at obscure and obsolete medical instruments in the Wellcome Wing. This is Clara's favourite part of the museum, but Conor has to be bribed with a ride on the space-flight simulator to get him past the shrunken heads on the landing. I'm not sure if he's still as scared as he was of the grim little sewn-up faces (which always remind me of Andie MacDowell, swinging from their hanks of ludicrously luxuriant hair), but Con's not about to lose the advantage of custom and precedent. He remarks, with a kind of boulevardier knowingness, that "Some boys don't like those heads," and I agree, just as airily, that shrunken heads aren't everyone's cup of tea. I then offer the space flight, as if this diversion had just occurred to me. Honour is satisfied.

We tour the glass cases showing scenes of Stone Age trepanning and medieval dentistry. But it is the obstetrics cabinet that leads to discussion. Clara is very taken with with the French ivory teaching doll, whose stomach lifts off to show the foetus in the womb. "I know where the baby comes out," she says, examining the doll's nether regions, "but how can something that big get through something that small?"

I have often considered this a design fault myself, but don't want to alarm her. "The mum's body changes when it's time for the baby to be born," I explain. "Yeah, can't you see?" says Con. Her tummy drops off, the baby climbs out and the doctor sews it back on again."

Clara shoots me a centuries-old look of superior feminine knowledge, but she's really no keener than I am to go into details. "Tell me about when I was born," she says. She's after the story of how, in the hospital ward I shared with three other women, I slept with her in my arms for three days, in case the other mothers, disappointed with their less marvellous babies, should try to swap. (The fact that two of them were black and one Asian could not, in my bonkers post-partum state, rid me of this conviction).

"What about the snake?" Con asks, pointing out the umbilical cord on the model. "Were we born cuddling a snake?" I explain about belly buttons and how, no, it doesn't hurt the baby when the cord is cut. "Actually, you're wrong," says Con. "I remember that happening and it did hurt. I was just incredibly brave."

"I expect you were," I say, shifting him to my offside as we pass the shrinkies again. I don't think I'm being untruthful. Confidence, at any age, is the story we tell ourselves.