Our younger son Toby turned two on Thursday, an occasion which he celebrated in time-honoured tradition by stuffing chocolate cake down his throat – and all over his face – with the kind of unselfconscious gusto that only a young child can exhibit. Although there is no mistaking the physical resemblance between him and his (four-year old) brother Isaac, anyone who has spent any length of time in the company of our two sons will know that they are very much like snowflakes. They may look identical at first glance, but a cursory examination soon reveals that they are more unlike than alike, particularly in terms of their personalities and preferences.

Heather has been suggesting we allow Isaac the opportunity to wash our cars for a while. Given that he is an avowed neat freak – borderline OCD, if you ask me – who thoroughly enjoys tidying up and helping us clean the house, it wasn’t exactly the biggest leap of faith to believe he might enjoy a bit of bucket-and-sponge work.

He has already moved on to thinking about Christmas, but Isaac turned four on Tuesday. Four! How quickly the time passes, and how quickly he continues to change. Reading back on what I wrote about him after his third birthday and then at the mid-point of his fourth year makes me realise just how much has happened in his life in barely 12 months.

I want my little boy back. It’s not that I’ve lost Isaac as such. But there is no escaping the fact that he is no longer the innocent little toddler which, in some way, he will always be in my mind’s eye. In his place is an increasingly aware boy who is fast discovering the reality of the world he lives in, with all that is good and bad about it. It is a double-edged sword, a bitter-sweet moment, and although I know I have to let go of his hand at some point, I am finding it one of the hardest things I have had to do as a parent so far.

Once a child starts to lose his innocence, you cannot put the genie back into the lamp. I know it has to happen eventually – but did it have to be so soon?