April DeBoer and Jayne Rowse walked past protesters Tuesday before talking to reporters.
"We love our children. This started out (about) our children. This is still about our children," said DeBoer.
View: Tuesday's courtroom blog
DeBoer has adopted a girl while Rowse has adopted two boys. Under Michigan law they are not allowed to adopt together because they are not legally married. Their lawyer, Carole Stanyar, told the court "these two women are heroes."
"Together they took in babies left behind -- special needs children. They loved all of them. They gave them what they needed. All of them are thriving," said Stanyar.
Her first expert witness was psychologist David Brodzinsky.
"It's not the gender of the parent that's the key. It's the quality of the parenting of whoever is there," he said.
Meanwhile, members of a group of Ypsilanti churches said they object to same sex marriage on religious grounds.
"The state of Michigan has already spoken on this issue. The people, the public has spoken and God has spoken," said Rex Evans, of Free Will Baptist Church.
In 2004 Michigan voters banned gay marriage.
"It's easy to get caught up in the sentiment and emotion," said Assistant Michigan Attorney General Kristin Heyse. "This case is about one thing. The will of the people of the State of Michigan."
But DeBoer and Rowse say they deserve the right to marry and be treated equally.
"Nothing says family like the marriage license that says that we are legally a family," said DeBoer.