CHI will take on the £4 million Kinder Bueno account, which was previously held by WCRS. It will create an ad campaign for the brand, due to run at the start of next year.
At the same time, WCRS has been handed responsibility for Rocher's flagship boxed chocolate brand, Ferrero Rocher. Its advertising has been handled in-house since it was pulled from Banks Hoggins O'Shea/FCB in 2002.
WCRS has recently created a handful of press and poster ads for the brand and it will now also take on the £5 million TV work.
WCRS already works on Ferrero's Tic Tac and Kinder Kids products.
The new appointments were made by Ferrero's marketing director, Dave Tucker. He said: "CHI's strategic insight and strong creativity will cement Kinder Bueno's position as a top-ten UK count-line and will help us move the brand forward to the next level of development."
He added: "WCRS will continue to contribute as a key strategic partner for Ferrero in developing great advertising which truly connects with UK consumers."
Ben Slater, CHI's new-business director, said: "We have been eager to form a relationship with Ferrero for some time and look forward to proving our ability with our big idea for Kinder Bueno."