Here's the scene inside a McDonald's in 1992. The restaurants was promoting Batman Returns, a Happy Meal campaign that led to some unhappiness. Batman Returns was a fairly dark film.
"I think I upset McDonald's," director Tim Burton reportedly said. "[They asked] 'What's that black stuff coming out of the Penguin's mouth. We can't sell Happy Meals with that!'"
From the Kids Meal Wiki:
A Dove spokesman said: Parents…trust McDonald's. 'So why is McDonald's promoting a movie to little kids that's filled with gratuitous graphic violence?
McDonald's Director of Media Relations Rebecca Caruso told the media The objective of the (Happy Meal) program was to allow young people to experience the fun of Batman the character. It was not designed to promote attendance at the movie. It was certainly not our intent to confuse parents or disappoint children.
According to Warner Brothers: Clearly Batman is not meant for 5-year-olds. As for whether it's appropriate to Happy Meals, that's up to McDonald's. We don't tell them their business.