The agency, which currently works on a retained B2B brief with Chewits, took on the contract after an approach for ideas from the company earlier this year.
The work is set to last at least a year and will involve a range of projects with the overarching theme focusing on getting adults to revisit the brand.
Cirkle chairman, Caroline Kinsey said: 'The brief is very much about generating consumer outreach and targeting mums - they’re the main audience for us in this case. The team is looking forward to getting mums and dads back on board and fully engaged with Chewits.’
The campaign will invoke childhood memories of places, fashions and flavours and will include social media and online promotion.
There will also be activity to support limited edition seasonal variants.
Hollie Roberts, UK consumer marketing manager at Leaf added: 'This is an exciting year for the brand and an opportunity to re-connect with parents. The on-trend nostalgic route Cirkle proposed is one we believe will really resonate.’