Most of them can’t really have understood what they were about to see

Most of them can’t really have understood what they were about to see. So the adult equivalent must be to have been dragged along to a gig in 1979, wondering why you were there at all, when suddenly out popped The Jam launching into “Down in the Tube Station at Midnight”.My son, who is just over two, has never been as ecstatic as he was in the following 90 minutes, partly because, in some respects, the show did follow the pattern of a normal rock gig. After the initial dumb-struck euphoria he, along with about 100 others, barged to the front by the stage and did that half-dancing, half-jumping thing you do at venues such as the Brixton Academy in south London. And to prevent the most exuberant from clambering under the stage, a line of muscular security staff in white T-shirts were posted in squatting positions at the front.There are some differences from gigs for adults. When you’re diving about to “Rage Against the Machine”, you tend not to have your mum behind you taking photos and warning you not to bump into the speakers.

And at Wembley on Sunday, during the interval, bouncers handed out hundreds of cardboard hats, which I don’t remember happening when I saw Nick Cave at the Shepherd’s Bush Empire.But how did the stars spend the interval? Does the actor playing Barney have a bigger dressing-room than the rest? And does he ever get artistically frustrated?It’s possible, because Barney groupies are too young even for pantomime games. Any subtle changes in choreography would therefore be lost, as would any attempt to develop the dark side of being a purple dinosaur 150 million years after the rest of his species have become extinct. The real purpose of the interval, though, is to provide an opportunity for parents and toddlers to stroll around the Barney programmes (pounds 7), Barney caps (pounds and fluffy Barneys (pounds 17). And with tickets at pounds 12 each, car parking pounds 7, and popcorn at pounds 2.50, if you’ve got more than one child it’s probably cheaper to go down to the Natural History Museum and put in an offer for a complete brontosaurus.In the second half, BJ announces what he’d like for his birthday. Knowing that they’ll be faced with demands for a similar present, you can feel 5,000 parents thinking: “Please say a Biro.”"I’d like a big red scooter,” he says.

Five thousand parents hold their head in their hands, and mutter: “Shit.”For a finale, BJ is presented with a 12-ft-high birthday cake. What a splendid thought, that if a child were presented with a 9-ft-high birthday cake, they might say: “Dur, it’s much smaller than the one BJ got from Barney.”Despite the expense, the hard-selling, and the banality, taking a toddler to see Barney is exhilarating. The calculated manner of Barney’s size, loudness and brightness connects with young children, and there he is, not just on a video, but in front of them, in real life. “I want to kiss Barney,” said my son – but I didn’t fancy his chances of getting past the security guards.”Is there any chance of meeting Barney?” I asked a particularly huge bouncer afterwards. “No, that’s finished, the exit’s over there,” he snarled in a monotone voice, while staring straight ahead, in the way American soldiers are supposed to shout, “I am a useless, weak piece of dirt, SIR!” at their sergeants.So Barney had left the building.

Maybe he was already on his way to a nightclub to do some coke.From an adult point of view, the whole show was not as bad as it might have been. Maybe it was scaled down for an English audience, but it was much less gooey than the TV version.And there was clearly no chance of an encore. Which didn’t bother me, as the closing number, his monster hit “I love you and you love me”, left me with a unique and unforgettable experience, of feeling two completely diverse emotions at the same time.On the one hand, there was the life-defining, overwhelming joy of watching your own child beaming and clapping in rapturous delight; and at exactly the same time, the thought: “I bloody hate that purple, poxy dinosaur.”. Some come because they’re miserable, others are into self-mutilation, a few are quite simply barking – all the time.