Monet Parham, a mother in California, filled the lawsuit against the fast food chain last week saying that McDonald’s is making it harder to encourage children to eat healthily by offering toys with its children’s meals.

“I object to the fact that McDonald’s is getting into my kids’ heads without my permission and actually changing what my kids want to eat,” she says.

Her case is being backed by the US Centre for Science in the Public Interest and follows a similar lawsuit in Wisconsin.

In a statement McDonald’s says: “We are proud of our Happy Meals and intend to vigorously defend our brand, our reputation and our food. We stand on our 30 year track record of providing a fun experience for kids and families at McDonald’s.”

McDonald’s claims that parents “consistently tell us they approve of our Happy Meals” and understand that they can fit into a balanced diet for children.

McDonald’s chief executive Jim Skinner recently told the Financial Times that the “food police” were trying to “dictate behaviour through legislation”.

Though this is a US only case, McDonald’s UK bosses and anti-obesity campaigners such as the British Heart Foundation, will be awaiting the outcome with interest.

Food manufacturers in the UK have increasingly been the focus of healthy eating campaigners who have accused them of marketing unhealthy foods to children.

Cereal manufacturer Kellogg’s has previously come under fire for including toys in its sugary cereal products and stopped including the toy giveaways in 2007, in favour of promotions based around family activities.

Kellogg’s also changed its marketing strategy so that it does not target advertising at children under six.