A study by the University of Glasgow has reported that people hugely underestimate the amount of sugar in drinks that are perceived to be 'healthy' such as juices and smoothies. This included not only fizzy drinks but also regular drinks such as apple juice and orange juice. They suggest that the average person in the UK consumes around 450 calories a day in (non alcoholic) drinks. That's amazing, that's roughly 2 chocolate bars worth of calories.
I remember buying a bottle of 'water' in a garage once to discover that it was 'flavoured mineral water'. It was made with mineral water and looked like mineral water but contained flavourings including sugar…so, er colourless squash then? Rather than 'water'.
On a serious note, we do have an epidemic of obesity in the UK, mainly affecting adults, but increasingly being seen in children. (Sadly with complications of obesity now being seen in children, like type 2 diabetes). Generally, the eating habits that you develop in childhood will continue into adulthood. So, if your child drinks water and eats healthily, they are likely to continue to do so as an adult. Equally, if they drink lots of sugary drinks and unhealthy snacks as a child, they will as an adult. I'm not saying that children should never have sugary drinks and treats, but that mostly they should eat healthily and have treats as treats.
Another thing to consider is their teeth. Brushing twice a day is great, but their diet also contributes to dental health. There is an increasing epidemic of dental decay in children (especially in Scotland, where the research was done.) Sugary drinks are among the worst culprits, along with sweets, particularly those that you suck. Once you have your second set of teeth, that's it, there are no more.
So, as Dr Seuss says "Don't gobble junk like Billy Billings. They say his teeth have fifty fillings!"
And don't be a sop, drink water instead of juice or squash or pop….