A mother doing her best to look inconspicuous is standing by the primary-school gates, whispering and eyeing up other parents. A slow and unsteady trickle of parents sidles up to her, take something quickly and stash it away, with much nodding and winking.

“Hurrah,” I think, the housewives are dealing temazepan again: have I any cash on me? Of course, all the woman is doing is handing out invitations for her son’s go-karting birthday party. I wait for the come-hither finger, but she blanks me, and then I remember that my son is not good mates with her son. It is a cordial, mutual dislike, and I give the mum a cheery wave, resist the temptation to say “It’s cool. Cut the cloak-and-dagger stuff,” and go to work.

My son attends a state primary school, where they don’t subscribe to the all-must-have prizes philosophy of party invitations. My richer friends who send their young children to fee-paying schools say there is an unwritten rule that a child having a birthday party must invite the entire class, or none. Depending on the school, this can mean 30-odd (and I mean odd) kids haring round the house in an e-number- induced frenzy, bursting into tears when the obligatory clown appears and going as green as the icing on the cake when the sugar-rush hangover kicks in. Or so I imagine.

“Oh, no, you take them places – such as the cinema or football parties,” says a mum of a seven-year-old who attends a school with such an unwritten policy. Since he was 4, her son has attended on average 22 birthday parties a year, and has had his own over-populated parties at all the acceptable venues. The bit she hates is that her already toy-swamped son gets loads more stuff, most of which she puts in a bin bag that she sneaks off to the charity shop, like a birthday version of The Grinch Who Stole Christmas.

But the sheer number of parties make some parents feel obliged to up the stakes. She mentions something that sounds like drag racing in the Seychelles, with plasma-screen TVs in the party bags. This mum is not for competitive extravagant party-giving, but even at the lower end of the budget, you won’t get much change from £200. It is worth it to see the grins on their little faces, she says. But is it?

If every child was invited to every party, what does that teach them about rejection and resilience, about choice and the freedom to like some children more than others, and to be liked more by some than by others? Who started this “come one, come all” madness?

Another mum who sends her daughter to a fee-paying school says: “It was OK until Allie was about 7 and she put her foot down and said she didn’t want a particular girl at the party because she would spoil it. I think that once they are old enough to make choices and express preferences, it should stop.”

Karen Sullivan, a parenting expert and author, says: “Even young children have the right to choose their friends. Inviting a whole class can be overwhelming, and a shy child might actively dislike crowds. As for self-esteem, there is no point in providing children with a false picture of the world around them; there will be times when they are not invited and they need to know it is not a personal slight. It’s life.”

Conversely, Michelle Elliot, of the anti-bullying charity Kidscape, thinks that exclusion could be seen as a form of bullying. “We get about 500 calls a year on our helpline about children being deliberately excluded from parties. One eight-year-old threw herself down the stairs because the class bully invited everyone to the party except her.”

Perhaps there was more to that situation than meets the ear. Yet it is clear that if parents of the privileged classes want to opt out of the whole-class party, they can just say “No”.

As for the children, they should be able to say: “My mum says I can have only six kids to my party.”

And for my son’s birthday coming up in a couple of weeks? Four mates for bowling and pizza.

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