Great, now all the undernourished kids with poor parents are going to drink water instead and lose weight to dangerously unhealthy levels.
According to The Guardian (same source as this article), the number of children in food poverty in the UK is 4 million. 15% of UK households went hungry in January. Now, soda isn’t the smartest source of calories in a kid’s diet. It’s expensive and low in other nutrients. But kids aren’t always smart. A poor kid thinks “I’m hungry, I have a few pounds, there’s a vending machine, problem solved”. If the soda is too expensive, that doesn’t mean the kid is going to go to Aldi, buy some potatoes, and roast them for a cheap and nutritious meal. They’re a kid! It means they’ll pay more or go without. Which means you’re making the poverty and malnutrition problem worse.