The appointment puts a question mark over Leo Burnett's future tenure of the £42 million account and comes at a time when McDonald's must confront the growing preoccupation with healthy eating.
Partners BDDH saw off Soul, BMP DDB and HHCL/ Red Cell to win the business in a pitch overseen by Agency Assessments.
The brief includes not only the Happy Meals assignment, which accounts for about 30 per cent of McDonald's business, but all other advertising directed at children.
The agency switch follows a traumatic period for McDonald's, which has suffered a profits dip for the first time.
Last month, McDonald's unveiled a new brand direction using the strapline "I'm lovin' it", which was developed by Munich's Heye & Partner, part of the DDB network. The company said the new strategy would be the "unifying element" for its forthcoming campaigns.
The theme will be implemented by McDonald's agencies worldwide, including Burnett in London and DDB in the US, which will apply their own style and approach in local markets.
At the same time, the company, facing flak for fuelling dietary problems among children, announced its intention to publish a guide, available in all its restaurants, offering tips to parents on making fruit and vegetables more attractive to children.