The agency's consumer team was selected following a three way pitch.
The account will be headed up by Fleishman Hillard's consumer team associate director Rachael Coomber-Nolan.
Fleishman-Hillard consumer director Louisa Jenkins said: 'We will be building the brand's status in the UK. Munch Bunch fits with our expertise, straddling our strengths in two key areas of food and parenting. We're combining our knowledge areas to develop an influential PR campaign.'
Munch Bunch offers a range of yoghurts and yoghurt drinks developed especially for children.