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If you're a kid who has two moms instead of a mom and a dad, what happens to you if they break up? Does one pay child support? Does she also get visitation rights?

The answers might be clear if your parents were a man and a woman who weren't married. But if your moms didn't register as domestic partners, what are everyone's rights in the eyes of the law?

That will be determined by the California Supreme Court (search), which is scheduled to hear oral arguments Tuesday in three child custody and support cases involving lesbians who parted ways acrimoniously after becoming mothers.

The court's handling of the cases is being closely watched by gay rights advocates and their opponents as a bellwether for where the justices might stand on a related social issue headed its way — whether same-sex couples in California should be afforded the right to marry.

The three latest cases center on whether laws crafted to protect children by establishing clear parental rights and responsibilities for absent fathers apply when the estranged couples consist of two men or two women.

Gay rights and children's advocates say the answer is simple: Adults who help bring children into the world with the intent of raising them should be regarded as parents, regardless of sexual orientation, marital status or blood ties.

Yet, lower courts — absent adoption papers or a formal domestic partnership — have shied away from recognizing the nonbiological parent in a broken, gay family.

"To the child, a parent is parent because that is the person who got up in the night and held them and put Band-Aids on their knees," said Deborah Wald (search), a San Francisco family law attorney with a large lesbian clientele.

"California is so clear about that when we are dealing with a mother and father, but when it comes to lesbian couples the courts have been the scalpel to remove children from the parents they deeply bonded to."

But lawyers for the three women whose cases are before the court argue the situations are not analogous. Laws intended to establish parentage in circumstances where both mother and father played a biological role can't be translated so easily to situations where conception required the use of reproductive technology, by necessity leaving one partner without a biological connection, they maintain.

In one case, for example, a woman who carried and gave birth to twins conceived with her ex-partner's eggs is trying to retain sole custodial rights because her partner signed a waiver at their fertility clinic relinquishing legal control.

It's unclear how many same-sex couples would be affected by the court's ruling. Many, if not most, gay men and lesbians adopt the children that were conceived with a partner's sperm or eggs to establish an unambiguous legal link.

And since a law took effect this year granting domestic partners in California nearly all the spousal rights of marriage, parentage has been presumed to apply equally to both mothers or fathers when children are born during the course of a registered relationship.

Nevertheless, gay rights advocates say the cases expose a fundamental inequity in the way California treats unmarried heterosexuals and gay couples who decide not to register as domestic partners or go through second-parent adoptions.

"Just like heterosexual parents, whether or not they are married, when a couple creates a child together they both take on responsibility to the child they created," said Jennifer Pizer, senior counsel for the Lambda Legal Defense and Education Fund (search). "Lesbian and gay parents should not have a free pass from those established family law rules."