Boychild's sixth birthday is over. It hasn't really bothered him that he shared his big day with Jesus but he is irked about two things: that the Easter Bunny is clearly suffering the effects of the credit crunch; and that his sisters get stuff on his birthday and he didn't get anything on theirs.

The twins have a big issue with sharing a birthday. Kate asked me how she could change her birthday. The only advice I could summon was that she marry Prince William, become Queen, and then she'll get an official birthday. She doesn't seem to think this will be a problem.

One of the best phenomenon of childhood is their unshakable belief that anything is possible. This weekend, while I've been struggling with Boychild's new lego set (that's another post entirely), Eve has been designing a rocket. She's told me it's top secret, so I can't disclose any details. She's worried that if the press get hold of it she'll have to fight through the Paparazzi every morning on the way to school. She's written to NASA and everything. She was so excited about the project that it made her cry, and that made me cry too. When she asked me to help her build it, I had to confess that I've never made a rocket before, and suggested she watch Apollo 13. There seems to be a film to address most parenting dilemmas.

But not this one. There is another topic Eve keeps raising with me that is even more challenging then making a plasma engine thruster out of a few planks of wood and a ball of string. She wants to know how babies are made, and she aint gonna be fobbed of with the when a mummy and a daddy love each other nonsense. I suppose I could let her watch Spouses Saturday Night Beaver DVD in the hope that it will put her off sex until she's at least twenty one, but even I recognise that would be yet another bad parenting decision.

She wants clear, clinical details, and I'm chicken. She asked me if you have to have an injection to get a baby... Kind of, I said. I knew this moment was approaching, stealthily from the murky depths of Twin 2's mind. I bought a book, but I'm too frightened to give it to her, because I can still remember the horror I experienced as a child when I realised that my parents did that twice in order to produce me and my brother. The other reason I'm resisting is that Twin 1 is happy as larry believing that babies appear, Zebedee like, as if by magic. And they are bound to share the revelation that willies are not just for weeing with Boychild. Jack had enough difficulty when he was about three and noticed that mummy didn't have something that he and daddy have. He looked at me in the shower one day, and, with tears welling up in his baby blue eyes asked, what happened to your willy mummy?

I guess I'm not ready to get off the magic roundabout of innocence yet, and Eve, sweetheart, you're gonna have to work harder to get me to spill.