Playmates: Bobby and John-Boy

Surely this must be a dream. Only in a dream could I be sitting in a converted church in south London with Bobby Ewing and John-Boy Walton. It's too surreal for waking life. While Bobby Ewing wanders away to get himself an apple, John-Boy Walton tells me of his passion for native American painting. It can only be a matter of time before my dead grandmother comes through the door, riding an elephant and playing the maracas.

The gentle pine-chopping and cornbread-baking of The Waltons was a world away from the camp melodrama of Dallas - but in its own way, just as much of a fantasy. What kind of conversation might they have, the sexy Eighties oilman and the dreamy teenager from 1930s Virginia? Are Bobby's tales of wheeler-dealing and extra-marital affairs in the big city terrifying John-Boy, whose only experience of scandal is the time Grandpa got drunk on stolen moonshine? Is John-Boy begging to hear more about the giant Oil Barons' Balls? No, he's giving Bobby the low-down on where to shop in London.

If Richard Thomas had changed at all in the 23 years since he left The Waltons, this might be slightly less weird. At least Patrick Duffy has managed to acquire grey hair. But Richard Thomas just is John-Boy: same floppy hair, same wire-rimmed glasses, same earnest enthusiasm.

To Duffy and Thomas, these long-running serials were simply acting jobs.

To me, and everyone my age, they were a whole childhood. How odd to hear them discussed by the protagonists in terms of "nuance" and "mise-en-scène." But they were just acting jobs, no different from the one which currently finds Duffy and Thomas in an overheated rehearsal room on the South Bank. In two weeks' time, they are going into Art in the West End.

But they're not doing the usual visiting-star splash.

"I don't know where the trendy places are, and I haven't seen a famous person yet," says Duffy. "I like quiet; if I find a restaurant with nobody in it, I'm happy. I get a meal, then it goes out of business." Thomas has done plenty of theatre; Duffy was "side-tracked by television" and has passed the years since Dallas in a successful sitcom which doesn't air here. But both are excited about their London stage debut.

"It's a very big deal for American actors," says Thomas. "I've been waiting to get asked to this party for a long time." "This is my cultural high point, playing the West End," adds Duffy. "My wife was in tears after the read-through."

Appropriately for veterans of quintessential family entertainment, their own families loom large. Some years ago, Patrick Duffy's parents were murdered by an armed robber who broke into their small-town post office, and the closeness of his wife and two sons (as well as his committed Buddhist religion) clearly helped him through this personal tragedy. His wife, former ballerina Carlyn, is here with him for the whole West-End run and they are writing a book together based on his other famous role as The Man From Atlantis. Their 25-year-old son is a playwright and their 20-year-old an actor - though somewhat more avant-garde than his old man, currently involved in a gender-bending production of A Midsummer Night's Dream.

Richard Thomas has recreated his Waltons heritage by acquiring a family of seven children. "I'm on the Planned Parenthood hit-list," he grins proudly. But, unlike The Waltons, it's a modern post-nuclear family including two step-children, triplets from his former marriage and a new baby with second wife Georgiana. Is it a pastoral bread-baking idyll? "Are you kidding? We have five teenagers and they're all girls! In our house we don't murmur 'Goodnight everybody', we shout 'Switch the goddamn light off!'"

Both men also retain family ties with their old TV colleagues. The Waltons kids are all grown-up actors, except little Elizabeth, who's a schoolteacher in Virginia, and Ben, who runs a courier business. Sadly, Grandma and Grandpa are now passing cornbread round the great pine table in the sky.

They were unusually well-adjusted child stars (eschewing drugs, the young Richard Thomas blew his salary on collecting art) and not one ended up in rehab or jail.

"I'm proud to say that we have no criminal convictions on our show," chuckles Thomas. "We all still support each other; we meet up at weddings, and they gave a baby shower for my wife. That show worked because the audience saw genuine caring between the cast."