For those unacquainted with modern childhood, the children's birthday party has changed almost out of recognition. The closest analogy is with the arms race, in which more and more money has to be spent in order for a party not to be deemed a failure. Our own birthday parties happen at home, with traditional games, but 24 party bags cannot be filled at less than £5 a bag and, even without an entertainer to add an extra £100-£200, there is little change left from £300 when all is said and done. Other parents hire the school gym or local swimming pool and get caterers in. We all laughed at the excesses shown in the film Mrs Doubtfire. Now they're here as well, and childhood is becoming an increasingly homogenised and, indeed, Americanised experience.
"The old English way was to have them at home, in which largely well-behaved children played games such as tag or hide-and-seek, followed by a formal sit-down meal in which children ate sandwiches first, then cake," says Susan Lee-Kelland, an educational psychologist. "Now there's a very American focus on consumption per head, per child, with lavish party bags at the end."
From the child's point of view, Britain is already the 51st state of the USA. They watch American videos, play American computer games, wear American clothes and, increasingly, eat and drink American food. Even if you resist branding with every fibre of your being, it is hard to escape. From the moment your child is in disposable nappies and drinking formula milk, their innocent gaze will be filled with cartoon characters from Disney and Time Warner. Having taught my own children to avoid anything advertised on TV as rubbish (why else would it need to be advertised?), I believed I had safeguarded them from Americanisation. Unfortunately, in doing so, I have also, in effect, isolated them. If your child would rather read books than watch Buffy the Vampire Slayer, certain social problems will inevitably ensue.
Virtually every high street in the south of Britain now has its own specialised shop for children's parties and toys, and British parents have increasingly succumbed to the frenzy of fashion to the extent that this year's in-toy (a Thunderbirds island) is currently unobtainable. The crazes that sweep through the playground have a maximum shelf life of three months, as Buzz Lightyear is replaced by yo-yos, yo-yos by microscooters, microscooters by Kitty. None of these toys requires the child to exercise any imagination, as Ted Dewan points out in his picture book Crispin: the pig who had it all. A wonderful satire on childhood consumerism, it shows its hero living in a minimalist house and getting ever more luxurious toys for Christmas. Eventually, he gets a huge, empty cardboard box from Santa which gives him "the one thing you do not have" - friends who teach him how to play.
Anyone who spends time with children can't fail to remark on how few of them do have a real notion of how to play or take imaginative possession of their toys, and how intimately this is intertwined with market value. My daughter is thought eccentric for cutting the labels off her (American) Beanie babies and renaming them, because every child of three and over is aware that this renders them "valueless".
It is arguable that the British concept of childhood as a time of innocence and purity from acquisitiveness has never been indigenous. As Lawrence Stone famously observed in Family, Sex and Marriage in England 1500-1800, we received many of our ideas on childhood innocence via the Romantics' interpretation of Rousseau. If you go to the Bethnal Green Museum of Childhood, you will quickly observe that most of the "traditional" toys that middle-class parents prefer were, in fact, originally German. Victorian wooden dolls and puppets and Noah's Arks came from Seiffen; to this day, the poshest teddy bears are by Seiff, though Brio, which makes outstanding wooden toys, is Swedish.
It is unfortunate that the bit of American culture which is exported is that of the mall. Yet America offers the world irresistible hopes and promises, alongside Coca-Cola - particularly for children, who have a strong sense of natural justice, and no experience to qualify it. Anyone who watches Disney cartoons will remark on the repeated messages of self-reliance, courage, disrespect for authority and optimism not to be found in, say, the animated tales of Beatrix Potter or even Wallace & Gromit.
Nick Park's Chicken Run, which parodies films such as The Great Escape by transposing them to a chicken farm, confronts this quite explicitly. The heroine, Ginger, insists on telling the other chickens the truth, even if this means depressing them with the news that they're all going to die unless they escape. The American "Lone Free Ranger" rooster is horrified. "In America, we have this rule: if you want to motivate someone, don't mention death." He himself appears to have mastered flight, but turns out to have been fired into the air by a circus rocket - a neat piece of cultural symbolism which unfortunately goes over children's heads.
If the benefits of Americanisation are less racism or fewer class distinctions, its evils are a loss of identity, of quiddity, of the capacity to relish or at least tolerate what is not instantly attractive. Modern children are increasingly rebellious about obeying authority, parental or educational: after watching Ariel the Little Mermaid (who, naturally, does not sacrifice herself and turn to foam at the end but gets her prince), defying her father and getting away with it, who can blame them?
They can see that Bart Simpson and his sister have more going for them than their washed-up, no-style parents: where British child-heroes and heroines typically have adventures away from parental authority, American ones now simply lack it. In the 1960s, American authors such as Edward Eager and Jane Langton wrote children's novels whose parameters were indistinguishable from those of British families. Now a bestselling American novel such as Louis Sachar's Holes has its hero sent to juvenile prison camp. His parents, like those of all the other inmates, are wholly powerless to protect or defend him.
J K Rowling may insist that Harry Potter should be played by a British actor, but even she could not prevent Hogwarts's terms becoming "semesters", or the title of the first book being needlessly changed from Harry Potter and the Philosopher's Stone to Harry Potter and the Sorcerer's Stone - philosophy, presumably, being deemed too scary for American kids.
If only more British authors had the guts to stand up to the lure of the dollar. One cringes for Evelyn Waugh who, at the demand of his American publisher, rewrote A Handful of Dust to give it a ludicrously happy ending.
Twenty years after American children began to be brand-aware about Levi jeans, our own children have learnt hyper-consciousness of the importance of having Nike trainers, Barbie gumboots and the latest groovy striped scarf from Gap Kids.
There are worse fates. I grew up with a number of American children and, despite being horrified by the habitual gratification of their every demand, I discovered that they eventually became polite, pleasant, if rather conventional, people. Perhaps the same thing will happen to our Americanised children. It's just that I would prefer them to enjoy free-range childhoods, rather than the battery-farm kind.
The author's new novel, In a Dark Wood, is published by Fourth Estate (£14.99)