Denny Smith just knew.

It was something about how Marie Wadman and Julie Ginsburg held themselves. It was the way they spoke, the way they looked. He spotted them at a meeting and felt absolutely sure -- instantaneously -- they were The Ones.

Five years later, Smith, who is gay, and the women, a lesbian couple, are raising two children together. Lucy, who's 3 and loves pink and hates wearing shoes, and Callum, a boisterous 1-year-old, live with their moms in a cheerful Victorian in Oakland. Smith, the biological father of both children, lives a few blocks away and takes the kids two days a week -- "daddy days."

All three consider themselves full parents and together they make decisions about schedules, holidays, doctors, religion, education and visits from six grandparents.

"I really loved them right away and I still love them," Smith said of his instant attraction to the moms, which he likened to cruising in a straight bar. "We have a great, great situation."

As the stigma against gay parenting erodes and more people take the baby plunge, the number of gay men and lesbians joining forces to co-parent is growing.

Though these kinds of creative families have existed for years, the increase is being driven by online resources, the enthusiastic example of co-parents and a greater willingness on the part of gays and lesbians to look beyond the nuclear family as a model.

The common denominator is that mothers and fathers are both involved in child-rearing, but the families come in various combinations of singles and couples and share parenting in a rainbow of ways.

"It's increasing by the week," said Stephanie Brill, an author of two gay parenting books and founder of an East Bay midwifery center.

Brill consults with families before preconception about everything from fertility to parenting agreements. When she went into business 12 years ago, prospective co-parents sought her help roughly once a month. Last week alone, she spoke with six sets of co-parents -- four from the Bay Area and two from other parts of the country.

"Ten years ago such family arrangements were very rare, largely because parenting by lesbians or gay men was really just starting to be a very serious and widely practiced option," said Kate Kendell, executive director of the legal organization National Center for Lesbian Rights.

Initially, she said, "I think many of us modeled a more traditional family structure. Over time ... many parents have exercised different options that give them and their child a wider network of support."

Co-parents can conceive at home at no cost -- with technology no more sophisticated than a syringe or a large eyedropper -- which opens the door to people who can't afford adoption, surrogacy or other high-tech fertility options, Brill said. "And more and more men are stepping up to the plate," she said. "This is where we're going to see the change."

Smith met the lesbian mothers of his dreams at a co-parenting matchmaking group in San Francisco called Prospective Queer Parents. Since the group was founded in 1991, about 15 sets of co-parents have found each other at the monthly meetings.

Smith usually has his "daddy days" on Wednesdays and Saturdays. One recent morning, he rang the doorbell at Wadman and Ginsburg's house. Callum jumped into his arms. Smith kissed him over and over.

"Little man, you look cute today," he said.

Ginsburg, 35, stuffed a bag while they spoke. Cal had a rash from blueberries. Did they need swimsuits? What time would they be back?

Finally the kids were buckled into their car seats and they were off to the playground in Alameda. "Bye babies," said Wadman, 42, waving from the sidewalk.

Smith is 52. He didn't feel ready for kids in his 20s or 30s, and now sometimes looks enviously at younger parents who will be in their prime when their children are adults. "This is where not being 32 comes in," he said, as he climbed to the top of the slide.

Smith had been looking for co-parents for years before he fell for Wadman and Ginsburg. He arranged to have coffee with the women at Cafe Flore in the Castro. They liked each other, so they agreed to meet each other's best friends and families to "rule out the ax-murderer scenario," Smith said.

They wrote out a contract -- one they haven't had to refer to yet -- addressing basic issues, such as how they would resolve conflicts.

Four months after meeting, they began trying to conceive. As they'd planned, Wadman gave birth to Lucy and then Ginsburg had Callum.

Only Smith and the biological mother appear on the birth certificates -- the law only allows for two names -- but in every other way they consider themselves a three-parent family.

Ginsburg, who stays at home with the kids, said she and Wadman, a tattoo artist, wanted their children to have a male figure in their lives.

"I'm adopted and I always thought it would be important to have knowledge of your biological family," Ginsburg said. "Parenting isn't what I expected, so co-parenting isn't either. Both are more intense than I expected. I think I have a warmer feeling and more of a sense that Denny is a part of our family than I might have conceptualized."

It doesn't evolve so smoothly for everyone. Making important decisions when three or four people are involved can be tricky and tedious. But before parents get to that stage, they must undergo the often excruciating hunt for the right partner with whom to forge this lifelong bond.

Prospective parents typically find each other through friends, newspaper advertisements, meetings or online listings. Many describe years of fruitless searching, near-misses and mishaps such as miscarriages or infertility.

John Maimone, a 37-year-old San Franciscan, eventually gave up. He had a thrilling "courtship" with one woman, but she dropped him when they got around to talking about specifics. Many women are fixed on having the lion's share of responsibility, Maimone said, and that's not what he wants. Now he's looking to adopt through surrogacy.

Daniel Owens, who has a 3- and 6-year-old with a lesbian couple, said that after his partner died of AIDS in 1994, he asked himself hard questions about what he wanted to do with his life. "I wanted something pulling me into the future," he said.

When he met the children's future moms, it was an all-out "love fest," he said. They moved ahead quickly -- in retrospect, too quickly -- and didn't put anything down on paper until after conception. They finally did sign an agreement, but only after lawyers got involved.

They're all satisfied with their arrangement now, Owens said, but it was an agonizing process because he felt then that he wasn't getting what he wanted. "It was a very painful, painful time and it was not good for the pregnant mother," he said.

Legally, co-parenting arrangements occupy confusing in-between ground. Traditionally, contracts between adults can't create or negate parenthood, said Deborah Ward, an attorney who specializes in nontraditional families.

Ten years ago, co-parenting contracts -- which can spell out everything from religion to baby announcements -- weren't considered legally binding. But surrogacy has thrown case law into question, and Ward now advises clients to take the contracts seriously.

In general, the law hasn't caught up with how families are being made in the 21st century, Ward said. "The biggest hurdle to these types of nontraditional families is that the courts are pretty stuck on the number two," she said.

Some California judges have granted third-party adoptions, which extend parenting rights to a third person. But most judges don't look kindly on them, arguing that they don't want to set up a child for a three-way custody battle, Ward said.

The domestic partner bill that goes into effect in California in January only muddies the legal waters. Under the new law, children born into a domestic partnership will be treated the same as a child of a marriage. But it's unlikely that will clear the way for legal three-parent families, Ward said.

In light of the legal uncertainties, good communication and honesty -- the same elements that make for successful marriages -- are critical, co-parents said.

"We certainly have a lot of trust and faith in each other," Ginsburg said. "We know the kids are safe. We feel he's caring well for them and he feels we're caring well for them."

When acquaintances learn of their family's arrangement, the reaction often amounts to, "Huh?" she said.

But "then they think about it and in a way, it makes a lot of sense," Ginsburg said. "It's an extended family that we're creating."

If their other extended families were thrown for a loop, they have long since gotten over it.