The agency's role is to handle media planning and buying for campaigns to back the spin-off merchandising from the Engie Benjy programme, the latest pre-school children's hit on CITV.
ZenithOptimedia won the business after a pitch process against at least two other agencies. It will plan and buy across various media, including outdoor, but there is unlikely to be any advertising on ITV.
The launch of the Engie Benjy consumer toy range will take place this autumn. The licensing programme includes 20 categories which cover books, computer software, jigsaw puzzles and clothing.
Engie Benjy is produced by Cosgrove Hall Films and uses CGI and other animation techniques. A second series of 26 episodes is due in the autumn.
Gary Knight, the executive commercial director of Granada Media, said: "I am delighted we now have a pre-school property on our hands that is destined to enjoy widespread success, both on air with our viewers and in store with our customers. ZenithOptimedia has shown real expertise in understanding the marketing needs of this franchise."
Tom George, the deputy managing director at ZenithOptimedia, said: "Engie Benjy presents the opportunity to explore a wonderful range of creative opportunities via our planning capability village@ZenithOptimedia, and we are confident of helping Granada drive considerable levels of merchandising sales."