The peculiar thing about this is that, if you make a polite protest or cast a disapproving look, all you get back is a mystified shrug and perhaps a muttered comment about the phone being on silent.
You realise that these people in their mid-to-late thirties simply have no concept of breaking any sort of taboo, or of annoying anyone else around them. They have no interest in, or understanding of, how theatre works.
Of course, their children are enchanted. But they won't be for long if they grow up like their parents, which is inevitable. And in twenty years time we won't have a theatre audience with an attention span of more than five minutes.
I sat directly behind a married couple and their two small children. Both parents consulted a Blackberry -- one each -- throughout the hour-long performance with their children -- one each -- on their laps.
Not only that, the parents were talking to each other in between Blackerry bursts. And, half-way through, the father, dressed like a Championship footballer in one of those black plastic winter jackets everyone's wearing this season, noisily got up, dumping his still transfixed (on the stage) daughter on the seat and clumped out of the theatre no doubt to fix a deal or buy a second-hand car he'd come across on e-bay in the dark.
I was so amazed by this I said nothing. But this week, as I head off to panto-land once more, I shall. And I think all theatres should make an announcement before every show, especially the toddler shows, that all mobile phones and Blackberries must be turned off completely throughout the performance.
The saddest thing of all is that the children are enjoying the theatre in isolation from their parents. And the parents are missing that special joy of sharing the delights of make-believe and fairytale with children for whom this experience is proving extraordinary and possibly life-changing. Yes, even at Bagpuss.
Like everyone else, I'm rushing around trying to do the shopping, the Christmas card writing, the partying and the end-of-year work that must be done before this time next week.
At lunch with neighbours and musicians yesterday, I learned of the BBC's plans to have a nationwide music festival on the first weekend in March mobilising every local orchestra and chamber group in the country.
It's the sort of obvious, all-embracing, inspirational brainwave that seems to have eluded the Olympic Games cultural provision planners so far. So, take a bow Susannah Simons, the force behind the splendid scheme.
It's all very well for Ruth McKenzie and her Olympic culture team to talk about European and American art house stuff like Robert Wilson's Einstein on the Beach (and how old hat is that, anyway?)...there doesn't seem, as yet, any idea whatsoever of involving people right across the land in sharing our deep-dyed traditions of amateur theatre, choral singing and street partying.
Perhaps if Ruth instigated a national "Blackberrying in theatres" day, that would do the trick: punters communicate with each other in the stalls creating their own alternative performance to the one actually being performed in front of them. But they must leave the children at home. This is the show that finally kills off theatre altogether.