The agency was selected ahead of Tullo Marshall Warren, Craik Jones Watson Mitchell Voelkel and Partners Andrews Aldridge.
The Department of Health's pitch was run by the COI and marketing consultant and former Boots marketing director Andrew Brent.
EHS Brann joins ad agency M&C Saatchi and media agency Manning Gottlieb OMD on the account, which will involve three years of marketing activity.
The anti-obesity campaign will be aimed at convincing parents to make changes to their kids' diet and increase their level of physical activity. It is part of the Government's Healthy Weight, Healthy Lives strategy.
Separately, Media Asia reports that Korea has approved restrictions on TV advertising for unhealthy food and drink products, following in the UK's footsteps.