The charity said the new work will reach out to its audience "in a new and distinctive way, inspiring them to support the cause and be part of the solutions".
The campaign is planned to run for between three and four years.
Last month Unicef launched "80 years apart", a film which weaves together a World War II refugee with a displaced child from Syria. The ad was created by 180 Amsterdam on a project basis, following last November's "It begins with a blanket" spot created by Saatchi & Saatchi.
Jennifer Walters, director of communications at Unicef UK, said: "We are facing an extraordinary period in history, with no end in sight for the ongoing refugee and migrant crisis.
''FCB Inferno's impressive strategic approach will deliver a powerful overarching campaign which covers many diverse and urgent issues, critically highlighting to the public that children are at the heart of this crisis. And that, with their support, we can have a real and significant impact on children's lives."