McDonald's, along with supermarket chains Rewe and Edeka and retail chain Tschibo, are members of the "Association for Consumer Education" which will soon start an education campaign in schools across the country.
And although the initiative was supported by Consumer Minister Ilse Aigner, consumer watchdog Foodwatch said the move made gamekeepers out of poachers.
"Rather than finally setting limits for the uncontrolled advertising machine for sweet and fatty children's junk food, Ms Aigner is easing the way into state schools for McDonald's and Edeka and leaving nutrition education up to them from primary school," said Foodwatch deputy manager Matthias Wolfschmidt.
He said the food industry already taught children unhealthy eating habits - something which parents and teachers were constantly encountering. "Edeka and McDonald's are experts in chocolates by the checkout and junk food, and thus are not part of the solution, rather are the core of the problem," he said.
Aigner dismissed the criticism, saying a study had showed teachers were keen to have businesses involved - as long as this happened in a transparent and neutral fashion.
She said the topic of consumer awareness was an important one for the whole of society, and that studies had shown serious problems with the way children and young people thought about what they bought.
The companies were supporting the campaign with a mid-five-figure sum, said Markus Mosa, vice president of the German Retail Association. "We want consumers who are not afraid to speak and who are aware of their responsibilities, and are aware that education is a considerable key for this," he said in a statement.
The firms involved do not want to exert any influence on what is taught in the schools, said managing director of the German Foundation for Consumer Protection Gerd Billen. His organisation is also involved in the initiative. He said sponsoring in schools was banned in most German states, and that schools were duty-bound to discuss such topics vigorously.