At seven and a half, my son still doesn't know about sex, or Sudan, or cancer, or calories. Though he has a reasonable knowledge of dinosaurs, earthquakes and volcanoes, and occasionally worries that one or all of them could pose a threat.
He used to want to drive a dustbin lorry. But now, when he grows up he wants to be one of those people who dig for things underground, though he has trouble remembering what one of those is called.*
And although I tell him he'll always be my baby - 'what, even when I'm a teenager? Even when I'm 100?' – he's unrecognisable from the baby that completely capsized my world all those years ago, bringing immeasurable meaning, joy and fear.
It was almost midnight when he arrived. He was sucked from my womb, blue and floppy, after a 40 hour labour. We were both exhausted. I should have slept, but I spent the night gazing at him with the light of my mobile phone, mesmerized by this tiny human being, a whole new person for whom I was now responsible.
And so, for the first few years of his life, I barely took my eyes off him – worried that I'd either miss something, or that something calamitous might happen.
Toddler groups became an exercise in separation anxiety. I'd plonk him in the middle of a train set, willing him to join in with the other kids. But he'd attach himself to my legs, or more frequently my boobs, in his resolute refusal to let go of Mummy, even in the face of biscuits and Thomas the Tank Engine.
I'd watch other kids tear around church halls, tip paint over the floor and shake the life out of soft toys, wondering why he didn't do the same, worrying there was something wrong.
Then, in an indisputable case of 'where did that time go?' J started school. He put on the obligatory uniform and we took the obligatory photos. Then we lead him into a classroom daubed in primary colours, and left him with a woman we'd barely met. And off he went.
I stood there waiting for him to turn around, cling to my legs, beg me to stay. But he didn't. He simply put down his bag and walked over to the Lego table.
And when it was clear he wasn't coming back, I faltered out of that classroom door, tears and snot oozing down my face, voice reduced to a helium squeak, feeling shattered and stupid in equal measure, while all around me other parents cheerfully waved and hugged their offspring goodbye. Or so it seemed at the time.
Yet, in a poll of 2,000 parents, taking your son or daughter to school for the first time, was voted most memorable and emotional moment of bringing up a child. Which makes me feel a little better. And for the record, I didn't just cry that first morning. I cried every morning for the next two weeks. And I don't normally cry - except when the hamster died in Charlie and Lola.
And then suddenly school just became, well, normal. And before we knew it three terms had passed. J had outgrown his uniform, worn out his Clark's shoes and learnt to read - albeit in a kind of monotonal, robotic fashion. And it was the summer again.
I remember taking him to a craft session one day during that first summer holiday. I hovered anxiously, protectively, behind him, ready to defend him from adult interrogation.
'I'm in reception,' J announced, when questioned about his schooling. And I realised I had nothing to worry about.
Now, as another summer comes to an end, it's impossible not to fear the years soaring inexorably by.
I watch as he splutters across the swimming pool, swipes at the monkey bars in the park, and orders an Appletiser without even glancing at me for reassurance.
J is changing – and not just in the darkening and unspiraling of his curls and the elongating of his limbs. He's letting go.
And I'm proud. And just a little bit sad. My boy is growing up. Beautifully.
In a few days' time, J will start school again, this time as a Junior.
For him, that first day of reception is now a forgotten memory, consigned to lost property along with all those water bottles, hats and plimsolls that he never did find. For me, it will always be one of the most emotional milestones of my parenting journey, and one that still chokes me now.
J says he doesn't want to go back to school in September - for him the summer is never long enough. But I know if there are any tears, they won't be his.
*Just in case you're wondering, it's an archaeologist.
More on Parentdish: Starting school - the first day