There can’t be too many parents around these days who fumble the answer to their children’s “Where did I come from?” question. But there are now thousands in the United States -- and elsewhere -- who have to put a lot more thought than the average parent into their replies. Those are the steadily growing numbers who are using surrogate mothers to provide them with babies.

The experts advise them to start early, reports the New York Times. One woman answered her 5-year-old twins’ question, “How is the baby made?” thus: “They come from a sperm and an egg. The doctor made you in a dish.” Another told her three-year-old daughter: “The doctor took a piece of Daddy and took a piece of Mommy and put it inside someone else because my tummy was broken.” Another intends to tell her two sets of twins that it is like using the neighbour’s oven because their own is broken.

A conservative estimate puts the number of surrogate births in the US at between 400 and 600 a year. Advocacy groups say the number is much higher. One woman, a lawyer who runs an agency connecting prospective parents with surrogates (having acquired three children that way herself), says her clients alone “had” 300 babies through surrogacy last year. Twenty per cent of those cases involved gay men.

Some parents tell their children all about the surrogate mother and introduce her to the children. “She comes to the door, and I’ll say, ‘Sarah, your surro’s here’,” says one mother.

A woman with older children whose surrogate was also the egg donor, rehearsed her story well, talking to the children about “Natalie” from a tender age. She reports:

“So when Lily was 9 years old, she said: ‘Mom, I have figured out that I’m not from your eggs. And I think Dad and Natalie make a pretty cute couple,’ ” recalled Mrs. Johnson, whose husband died several years ago. “I said: ‘Lily, well, Natalie and Dad were never a couple. You were only created in the doctor’s office because I was going to be your mother. Would you like to see your birth certificate — because I’m going to be your mother forever.’”

The story gets even more complicated when a same-sex couple is involved:

Jeffrey T. Parsons, a Manhattan psychologist and his partner, Chris Hietikko, have a 3-year-old son, Henry, who sees his surrogate, Jessica, at least once a year. When their son starts asking questions at, say age 5, said Dr. Parsons, a psychology professor at Hunter College, “I would probably relate it to one of his friends. I’d say, ‘You’ve met your friend Michael’s dad and mom. You have two dads, right? Well, it takes a mom to make a baby because they grow them in their tummy. That’s Jessica.”

Well, we don’t know what Lily is saying about it now that she’s 19, or what Henry will say when he is old enough to have his own ideas about being produced to make two men happy rather than conceived by his very own mom and dad, but the odds are that there will be some very resentful young adults around soon as a result of this manipulation. Then what will they tell them?