The Mothercare Group, which owns the Mothercare and Early Learning Centre brands, has charged Diffusion with developing a social media strategy to target parents on and offline.
The collective online voice of parents has reached such a level of influence that this year's general election was christened the 'Mumsnet election' in the press, with politicians openly courting online groups.
Figures from market research agency comScore showed 4.6 million mothers in the UK turned to online resources every month, spending 26 hours surfing the web.
Diffusion will work with Mothercare to listen to perceptions of brands and products and to help it participate in the relevant communities on key parenting blogs, forums and social networking sites.
'Busy mothers today are consuming an increasingly complex media diet from breakfast TV to blogs,' said Diffusion MD Ivan Ristic. 'Brands like Mothercare must take an integrated approach to their communication campaigns to achieve meaningful message cut-through.'
As part of the brief, Diffusion will also raise awareness of Mothercare's social networking community for new parents, Gurgle.com, via mainstream print media and broadcast channels.
Ristic added: 'Our campaign will not only look to develop a positive narrative for Mothercare in these important parenting blogs, forums and social network groups, but also integrate with traditional media activity and events to drive more footfall to Mothercare stores and sales to mothercare.com.'
Brian Curran, head of group direct marketing for Mothercare, said that the appointment would 'allow us to enhance and safeguard our online reputation and increase our ability to listen to our consumers to deliver even better products and service'.
Mothercare previously handled comms in-house.