"Wonderstruck" is an adaptation of Brian Selznick's young adult novel about two kids who run away to New York.
At an emotional press conference at the world's top film festival, director Todd Haynes, who bewitched Cannes critics with his lesbian love story "Carol" two years ago, shed a few tears of his own talking about working with Moore, Michelle Williams and their child co-stars.
"Wonderstruck" is an adaptation of Brian Selznick's young adult novel about two kids who run away to New York, one in 1927 and the other in 1977.
The title refers to a lushly illustrated book left to a young boy after his mother (Williams) dies.
The volume offers clues to the identity of the child's missing father, leading him to slip away from his home on the Great Plains and hop on a bus to the Big Apple.
But before he leaves he is struck deaf in a freak accident and must make his way through the urban jungle without being able to hear.
A separate strand of the movie is set half a century earlier in which a girl, played by deaf actress Millicent Simmonds, goes searching for the actress' mother (Moore) who abandoned her.
The stories eventually interwine, as Haynes recreates the bustling energy of pre-Depression New York and the urban blight and seething sensuality of the 1970s.
"This was all about imagination -- the vitality, the challenges, the complexity of kids," Haynes said.
"I think (kids) can handle a film that has this kind of complexity and dimension to it."
It marked the fourth collaboration between Haynes and Moore, whom the director called his "creative soulmate".
Moore said it was an "extraordinary opportunity" to play "two different parts in two different time periods," and learned sign language for the movie.
"For me as a hearing person this was my first experience with deaf culture," she said.
"The people who understand those cultures are the ones who've been in both rooms. I didn't get to be in both rooms but I was allowed to stand in the doorway and what that gave to me as an individual was tremendous."
Williams, who was nominated for an Oscar this year for her role as a grieving mother in "Manchester By the Sea", said being a single mother to her daughter Matilda with the late actor Heath Ledger taught her to respect child actors' talents and needs.
"For Mother's Day this year my daughter gave me a card and it said 'Mom, thanks for letting me be me' and it was a picture of somebody in high heels on a skateboard," she said.
"That's what I'm looking to do, I'm looking to respond to these children in the moment with what they are really offering me."
Haynes's "Carol" drew six Oscar nominations though it came up dry on awards night.
Industry magazine The Hollywood Reporter said "Wonderstruck" looked headed for Academy Awards nods too, while US movie website Indiewire called the movie "exquisite" and an "immaculately crafted fable about the ways in which people of all ages learn to break out of their bodies and connect with the world".
A moved Kate Muir of The Times of London tweeted she needed a "full mascara re-application" when the lights came up.
Other critics were less impressed, however, with Variety calling it "a lovingly crafted adventure of innocence that winds up being less than the sum of its parts".
And the Guardian's Peter Bradshaw declared himself "disappointmentstruck" by an "indulgent and supercilious" movie.
"Wonderstruck" is among 19 films vying for the coveted Palme d'Or top prize.