SAN FRANCISCO — When Supreme Court Justice Anthony Kennedy invoked the interests of children during oral arguments on Proposition 8, email boxes at the Family Equality Council began lighting up. "Oh my god, Justice Kennedy has just asked the most beautiful question," said one message.

The D.C.-based organization and its outside counsel at Bryan Cave have been trying to ensure that, as the high court weighs the right of same-sex couples to marry, the justices don’t overlook another group of interested parties: the children of couples who can’t wed.