DETROIT -

Two Detroit-area nurses challenging Michigan's ban on gay marriage entered the courthouse hand-in-hand for the start of trial on Tuesday.

In 2004, the state of Michigan enacted the Defense of Marriage Act after it was passed by 59 percent of voters. The act argues that children benefit from living in homes of heterosexual couples.

View: Monday's courtroom blog

But nurses Jayne Rowse and April DeBoer filed a lawsuit, saying the amendment violates the U.S. Constitution's Equal Protection Clause, which forbids states from treating people differently under the law. Bu the state of Michigan says there's no "fundamental right" to marry someone of the same sex.

DeBoer and Rowse have three special needs children who they foster because they cannot legally adopt the children together under Michigan law.

“We love our children. This started out about our children. This is still about our children," DeBoer said. “Nothing says family like the marriage license that says we are legally a family. That’s what we’re hoping for.”

During a trial that starts Tuesday, the state is expected to have experts testify on the emotional and social outcomes of children raised in same-sex households. 

Related story: Michigan State studies health of same-sex couples

The trial will be the first of its kind to include scientific studies on same-sex parenting. The state attorney general's office says heterosexual marriage provides the best family setting for children. Attorneys for Rowse and DeBoer say research shows there's no difference for kids in same-sex households.

Related story: Couple fights Michigan ban on same-sex adoptions