Why I'll miss those magical days playing with the kids
I can now count how many more days my son and I will be alone together, just the two of us, on one hand. His time as a nursery pupil is coming to an end and after that he'll be on the same schedule as his sister at school.
Mums and dads around the country will understand how that feels but for those whose children are still years from school age I urge you - make the most of every private moment you can share with your sons and daughters because when it's over it really hurts.
I didn't quite appreciate the full picture with my daughter. We had nearly four years of just hanging out together before my son was born.
I loved that period of my life. When I think of it now I see it through a sort of blissful haze.
We were a double act, doing everything together every day; shopping for cupcakes, wandering round the local petting zoo, reading together at the library.
Some friends of mine have told me they found their toddler children a bit stifling, rather trying, tough work.
I'm completely sympathetic - to be honest, before I had one I suspected I might feel that way too. But I was lucky - I loved (almost) every moment. I found patience I never knew I had (major revelation for my family).
I gave up office life permanently to work at home so I could fit in everything around my daughter, and it didn't occur to me that once my son came along, and she went to school, we'd struggle to squeeze in whole days of the kind of mother-daughter time we used to take for granted.
This time around, I know the score, and as my four-year-old son says goodbye to his nursery days, I find myself increasingly, disarmingly sentimental about every little thing he does, and we do together. I torture myself like a masochistic mumzilla.
No more sunshiney days when we wander off to a quiet park together so that he can show me how fast he can push the roundabout on his own.
No more larking at the swimming pool with almost the whole place to ourselves, me trying to get him to concentrate on how to close his hands doing the breast stroke while he tells me which sea monster he's currently portraying.
Time is passing, the voice inside my head goads. He can write his own name now. He can pronounce 'yellow'. He'll be back-packing across Australia and never phoning any day now.
Which is why last night, when he slipped out of his own bed and noiselessly into ours, I didn't carry him back to his room like I'm supposed to, but instead lay gazing at the inch-long eyelashes resting on his freckled cheeks while he fell back asleep.
I don't know if he'll really notice the change - though his sister does still talk about the days when "it was just you and me mummy, and we had girlie days out every day". And of course, as she and I do, there will be times when I make a point of stealing him away for a few hours so I can have him all to myself.
But a change is gonna come, and I'm pathetically emotionally unprepared.
I just hope that he remembers just a fraction of what I will always think of as some of the best years of my life.