There isn’t a parent in the land who hasn’t wondered how “fine” they would be in those circumstances. Sometimes the possibility is discussed openly; more often it is a concern kept to oneself; a bridge to be crossed on another day, or not at all.
On one level, we know that we would indeed be fine, because our children’s happiness matters more than our own.
But parents in their middle years and above, myself included, are caught in a generation gap. We grew up in an age when to be gay was to be stigmatised. In some families, that is still the case. The charity for whom Prince William spoke was one that helps young people made homeless because of their sexual orientation. Is there anything more unnecessary than that?
It is one of the more heartening aspects of life in the 21st century that a tide of tolerance is gradually washing away the residue left by years of repression. But it is a slow process. Half a century has already passed since homosexuality between consenting males was decriminalised. That law saw off the era of the blackmailer but not of the bigot.
This century has brought a faster shift in attitudes, accelerated by the disproportionate noise of social media. The bounds of behaviour have changed; conventions which were acceptable not long ago are now repugnant. This in itself can be frightening. Change can come only at a speed at which people can comprehend it.
But that is exactly why William’s intervention struck such a chord. He understood that the issue is rooted in the family, not in the political jargon of same-sex marriage and gender-neutral bathrooms.
Tolerance, like charity, begins at home: if we can embrace the lifestyles of those closest to us, it is harder to look askance at anyone else.
It is easier said than done, for we are all products of our upbringing. William expressed a concern as to how society would perceive his children if they were gay, and it is one that will resonate with anyone who has brought up a teenager, or tried to – for we knew how the world would have treated us, three or four decades ago.
Those with similarly long memories will recall how it treated the Duke’s uncle, Prince Edward, who was for years the victim of needless innuendo which, if it were levelled at our own children, would horrify us.
Many of today’s schoolyards are enlightened places, where it is the norm for teenagers to question their gender identity in the knowledge that they are free not to conform to a stereotype that doesn’t fit them. This is progress, it seems to me, so long as their parents are on the same page.
Tolerance is not universal, however. Just a few hours before William spoke, a 12-year-old boy was arrested elsewhere in the country on suspicion of a homophobic attack on two men.
That sort of thing belongs not in the present day but in the bygone era of homosexuality we are seeing dramatised in the wonderful Gentleman Jack on BBC1. Closeted away at Shibden Hall in Halifax in the 1830s, the businesswoman and traveller Anne Lister had to consign the details of her life to coded journals, such was the social impossibility of declaring herself a lesbian.
The road from Ms Lister to Prince William has been two centuries long, but the rest of the journey may take only a single generation, if the Duke and people like him continue to publicly advocate tolerance that is born of understanding, not of being dragged along with the tide.
Coming in a week in which we learned that his brother had spent £2.4m of public money on renovating his home, we needed to be reminded of the force for good that the modern Royal family can still be – Harry and Meghan included.
This weekend marks the 50th anniversary of the investiture of Harry and William’s father as Prince of Wales, and Charles has spent much of the intervening time campaigning for the environment. He was once dismissed as a crank, but most of us realise now that his concern is ours, too.
William’s message is even closer to home.