Parent sends child to school with cold McDonald's Happy Meal for lunch.

The McDonald's, bought the previous night, has been labelled by staff at Byron Primary School in Kent as extreme and worrying. Photo / Getty Images

As a parent, you'll likely have experienced that moment of panic when you're desperately trying to get your children out the door for school, only to realise they have no lunch, and the cupboards are empty.

Parents at a UK primary school have been criticised after finding themselves in this exact predicament and opting to send their child to school with a cold McDonald's Happy Meal as their packed lunch.

The leftover meal, bought the night before, has been labelled by staff at Byron Primary School in Kent as "extreme" and "worrying", according to reports.

As well as the McDonald's lunch, the school also contacted and offered advice to parents who filled their children's lunch boxes with chocolate cake, chip sandwiches and smarties.

Parents at the school were both shocked and amused at the letters they received, posting on social media to vent their frustrations.

However, not all parents were against the school's lunch box interventions, with one mother showing her support by stating:

"We've all woken up in the morning and realised we don't have stuff for packed lunch or money for school dinners, but surely there was something else in the cupboard. McDonald's Happy Meals cost more than school dinners anyway. The school is clearly trying to educate the parents which I think is brilliant."

This isn't the only time parents have been in the spotlight for their lunch box choices. A school in Missouri sent home a note to parents after they sent their daughter to school with four chocolate bars, a bag of marshmallows, Ritz crackers and a pickle.

An Australian mother also received a note from her 3-year-old's kindergarten teacher, telling her to stop sending her child to school with homemade chocolate slice, as it was in the Red Food category.

A friend of the family took to social media to stick up for the mother-of-eight and share some words of wisdom.

"I told her to put in two slices tomorrow and tell them to get lost."