The agency is launching its first work towards the end of the year, and a TV ad will go live in January.
Bear Nibbles makes cold-pressed fruit snacks aimed at children. Products include Yoyos, Paws & Claws and Alphabites cereal.
The brand was founded in 2009 by health food brand Urban Fruit, which was acquired by Lotus Bakeries in December 2015.
Emma Howgego, marketing director at Bear Nibbles, said: "It was really important to us to find a brave, honest and exciting agency to help us create a campaign that feels truly Bear."