The two charities have tasked the independent agency with working to encourage families, and in particular parents, to improve children's language skills through a series of behavioural nudges.
Confirmed last week, the contract is for an initial 12 months.
Founded in 2009, 20-person agency Claremont was recently awarded a place on the Government Communication Service roster as a behavioural specialist. Other recent and current clients include the Alzheimer's Society, the Government's apprenticeships service, the relationship charity One Plus One.
Tom Rahilly, director of UK programmes at Save the Children, said: "Hundreds of thousands of children across the UK are behind in their early language development when starting primary school and more often than not these are children from low-income families, which is just plain wrong. Our aim is to help every child become confident communicators to lead happy, fulfilled and successful lives.
"This campaign will deliver sustained positive change to children’s home-learning environments, in a way that is easy and accessible for parents," he said.
Claremont has called in research partner Audience Communications and behavioural scientists The Behaviouralist to address specialist aspects of the project.
Adam&eveDDB remains Save the Children's lead brand and creative agency.