Bryan Alexander

USA TODAY

Robert Lopez and Kristen Anderson-Lopez wrote eight songs for %22Frozen%22

The movie showcases the song %22Let It Go%22 featuring a version by Idina Menzel and Demi Lovato

Daughters Annie%2C 4%2C and Katie%2C 8%2C also have voice parts in %27Frozen%27

Early on a recent November morning Annie Lopez, 4, was walking with her family on Hollywood Boulevard when she spotted a large billboard for Disney's Frozen.

"There was a guy walking by who clearly had a rough night," her mother Kristen Anderson-Lopez recalls. "And Annie was like, 'See that billboard for Frozen? We made that movie!'"

There is some definite childlike enthusiasm in Annie's statement about the animated musical fairy tale directed by Chris Buck and Jennifer Lee, which features the voices of Kristen Bell, Idina Menzel and Josh Gad.

But the Lopez family certainly had a large part in the film (opening Nov. 27), namely through Anderson-Lopez and her husband Robert Lopez, the songwriting team that composed Frozen's eight original songs — including the triumphant Let It Go sung by Menzel in the film along with another version performed by Demi Lovato.

For the Lopezes,

"There's not much the Lopez clan cannot do, they are disgustingly gifted," says Gad, who worked with Robert Lopez on the Broadway hit The Book of Mormon. "It would seem that this kind of collaboration could get in the way of a marriage. But for some reason it only seems to support and build their love for each other. And they put that love back into their music in a way that's astounding."

The love began in November 1999 at a New York forum for writers and musical theater. When Robert Lopez performed an early version of a song from his musical Avenue Q in a yellow yarn wig, Anderson-Lopez was transfixed.

"It was kind of humiliating, but Kristen really liked it," says Lopez.

"It really was one of those moments, when he walked in. I was like, 'I love him, I am going to marry him,' she says.

Avenue Q would go on to win Lopez a Tony Award and the two married in 2003. When Anderson-Lopez was approached to work on the Walt Disney World production of Finding Nemo — The Musical in 2006 the couple embarked on their first full-time collaboration.

"She was invited to find any composer she wanted. And she picked me," says Lopez.

"I was like, 'I hear about this guy Bobby Lopez, he just won a Tony. And he's standing right here,' " says Anderson-Lopez.

Taking on the task of writing the music for Frozen required daily, two-hour conference calls with the film's directors starting in January 2012 to help flesh out the characters. Still, the songwriters had a parental advantage in the tale about two loving sister princesses at odds with each other.

"That really resonated for us, having two daughters. Our youngest just thinks our oldest is a superhero. And our oldest is often like 'Leave me alone.'" says Anderson-Lopez. "We knew exactly what that older-younger dynamic is."

There were frustrating moments in the creative process ("it definitely can be full of angst," says Lopez). And the two sometimes have to separate work pressure from home frustrations. "Sometime it's like, OK, 'What's going on here?' It's not about a lyric is it? It's about your mother,' " says Anderson-Lopez.

They broke through on Frozen and the raves are rolling in. Playlist called it "a new Disney classic" and said "the most endearing aspect" of the film was the couple's songs. Let It Go also is enjoying front-runner status for Best Song award contention.

The duo are not exclusive writing partners ("we're promiscuous only so far as work collaboration," says Anderson-Lopez). But they plan to continue working from their Brooklyn home on a yet-to-be announced Disney project and a stage production called Up Here.

"The only bad thing about being a husband and wife team is, when things aren't going well, you cannot go home and complain to your spouse," says Lopez, who says he still breaks open a bottle of expensive champagne every wedding anniversary to give thanks for the partnership.

"I get to play all day with my best friend, and he also happens to be my favorite Broadway composer," says Anderson-Lopez. "We're both very, very grateful."