It's lunchtime in the leafy grounds of the Kairos School of Inquiry in Randburg, South Africa. Dozens of children line up excitedly in front of a table laden with large pots of fresh, hot food.

Today on the menu we have Kitchari: a mix of daal and rice, with tomato chutney, halloumi and salad, the school cook says, as she serves the students. The school decided to introduce a mainly vegetarian food policy as part of an effort to buck a worrying global trend: for the first time, the number of overweight children has overtaken the number of underweight ones.

The UN says the number of overweight and obese teenagers around the world has nearly tripled in the last two decades. The number of overweight children aged five to nine years old has increased from 69 million to 147 million.

Parents at Kairos have been asked to pack only whole foods in their children's lunchboxes. Headteacher Marc Loon believes the policy has provided an opportunity to teach students about the importance of healthy eating.

If all schools were to emulate our intention of being thoughtful and conscious of what children are putting into their bodies... the health of the children would be served, he said.

However, the growing popularity of convenience food in the developing world is partly responsible for the rise in obesity rates amongst children, according to UNICEF. Families often face a dilemma when it comes to food choices; easy access to fast food can overshadow healthier options.

Pupils enjoy nutritious meals at school, yet figures reveal a stark reality: 22% of children under five are now overweight or obese in South Africa, up from 13% in 2016. Many families struggle to afford healthy food despite the country being deemed food-secure, highlighting the urgent need for policies that provide access to local, nutritious options for children.

Until such measures are implemented, schools and community advocates like at Kairos are crucial in safeguarding the health of future generations, emphasizing nutrition and awareness in the fight against childhood obesity.