Kids' meals at two major fast-food chains in San Francisco became slightly healthier after a 2010 law was enacted, suggests research from the University of Washington.

Although the changes at the chains could not be directly attributed to the law -- both simply sold kids' meal toys for 10 cents instead of giving them away, as the law had banned -- the kids' meals got healthier, said Jennifer Otten, assistant professor of health services in the School of Public Health.

For example, McDonald's cut the serving of french fries in Happy Meals in half, replacing them with apples, reducing the meal's calories, sodium and fat content.