A child with three (legal) parents? Don't blow a gasket yet...
News that the California assembly is considering a law that could recognize more than two parents for a child is already causing a bit of a dust-up on the "what makes a family front," with Rod Dreher of the American Conservative  already out of the gate: "This is an attempt to accommodate the radical irregularities in modern childbearing practices (surrogacy, etc.). What would this law teach us? That there is no such thing as the natural family — that family is whatever we say it is."
A closer reading, at least of the Sacramento Bee story  Dreher and I both read, might suggest a little less dramatic reaction. Quoted from the Bee are three situations in which the new law (versions of which already exist in Maine, Delaware, and Pennsylania) might apply:
• A family in which a man began dating a woman while she was pregnant, then raised that child with her for seven years. The youth also had a parental relationship with the biological father.
• A same-sex couple who asked a close male friend to help them conceive, then decided that all three would raise the child.
• A divorce in which a woman and her second husband were the legal parents of a child, but the biological father maintained close ties as well.
Considered in light of these situations, the last of which I imagine could be quite common, one begins to see the purpose of the law, which simply put is to protect the interests of the child. (The law was meant to remedy the situation of a child who ended up in foster care because the state would not recognize the child's biological father when the child's mothers, a same-sex couple, were unable to care for him.)
Dreher worries that such a law would diminish the church's ability to "teach" what a natural family is; I on the other hand agree with Thomas Aquinas in arguing that the primary purpose of the law is ensuring justice--in this case, protecting the child.
That's why it makes sense to allow people to create legal families that don't fit Dreher's "natural" two-parent form: Many children don't live with their once-and-still-married biological parents. Should they not have the protection of the family law just because their family doesn't meet a certain ideal? That doesn't sound just to me.