And with many schools accepting thousands of pounds a year from fizzy drinks companies in return for installing vending machines in their corridors, it’s hardly surprising that most kids don’t drink enough water.

“Low levels of dehydration can have an effect on mental performance,” says Dr Lunn. “A study at Leeds University showed that children’s ability to do arithmetic was impaired if they were between one to two per cent dehydrated. That’s not even enough to cause feelings of thirst.”

So what’s the solution? Go back to basics, says dietician Amanda Ursell. “Eat like your grandparents,” she says. “Cook plain food like porridge for breakfast, fruit and pitta bread for lunch, chicken and vegetables for dinner. Learn to understand food labels.”

And however busy you are, make sure your child eats regularly. Breakfast is particularly important. “Research has shown that eating breakfast may improve children’s problem-solving abilities, memory, concentration levels, visual perception and creative thinking,” says Dr Lunn.

Olivier believes we should also teach our children more about the wonderful world of real food. “Our children’s tastebuds are blunted with salt and sugar,” she says. “They should enjoy and appreciate real tastes and textures – not artificial ones.”