Once upon a time there were three bears. Not, as the story would have it, a mummy bear, a daddy bear and a baby bear, but three identical bears. And they lived, not in a cottage in the woods, but in a cot or a wardrobe, depending on which point of the rotational cycle they were at.
When one bear was beginning to look a little past his prime he would be whisked off to rehab and replaced, in the dead of night when small people were snoring, by another bear, slightly fresher perhaps, but in all other ways indistinguishable from his cohort.
The happy ending to this story is entirely dependent upon this cycle of strict rotation, ensuring that no bear remains pristine and smelling of "new", and all become interchangeably bedraggled at the earliest opportunity.
There is, perhaps, no finer illustration than this of the benefits of being an older mother. You inherit the wisdom and experience of all the friends who've been there before you and sometimes, just sometimes, you learn from their mistakes (in this case, never to underestimate what the loss of an offspring's favourite toy can do to your nerves and your sleep patterns)
It is thanks to such insight that a small girl of my acquaintance is never parted from her beloved friend, even when unforeseen and unfortunate incidents occur - although I am sure there will soon come a time when she will understand that her parents' vomit-removing capacities are duplicitous rather than super human.
Perhaps I should confess that this popular ursine fable is not the only tale to have been tinkered with in our household.
Take the old woman who lived in a shoe. I really don't want to paint my daughter a picture of scores of children being whipped soundly before turning in for the night, so our version has the over-fertile crone reading them a story before they trot off to bed. Still without any bread, after all there is tampering and there is tampering. Dr Atkins would be proud.
Looking at them anew, this time from an adult perspective, it becomes clear that the majority of nursery rhymes are not terribly child friendly. To say the least.
Oranges and Lemons? Decapitation. London Bridge? Beyond repair. Three Blind Mice? Dismembered. And so it goes on.
These days it seems that every time I open our book of traditional rhymes and ditties I find myself getting a little maudlin. It may, of course, be my hormones, but that doesn't stop me shedding a tear for all those poor people falling down dead from the plague in Ring o' Roses.
Then there's the misfortune befalling the innocent folk of Gloucester, left without any medical cover all because Dr Foster didn't have the perspicacity to look where he was going.
And what about that poor maid, left to do all the chores while her fat-cat employers count their cash and stuff themselves silly on sweet treats? All she gets by way of thanks is the loss of her nose. Although I can't say I really blame any blackbird that has the fortitude to make it through the pie fiasco unscathed for being just a little bit narky. Who'd have thought that reading children's stories could be such a minefield? Last night I spent half an hour comforting my weeping toddler who had taken a singsong session too much to heart.
"Poor Humpty Dumpty" she sobbed. "Fell down banged 'is 'ead. Broken."
That's not to say that there are no tales more suited to my sensibilities: as it happens I am in total accordance with mummy cat's position of no pie, for if the little kittens have lost their mittens they surely need to learn that carelessness has consequences?
But for the sake of all our nerves, I think we'll be sticking exclusively to Twinkle Twinkle for a while.