They should imo be banned for EVERYONE not just kids and quite a few are in other countries, the Uk is woefully lax on understanding and regulating things regarded as food or drink.
Why are they harmful?
In simple terms:
They rot your digestive system (from the tongue down! I've met patients who've had to have all or part of their tongues removed due to the damage done by drinks like this inc excessive consumption of cola drinks, also parts of lips and palate and of course rots your teeth - very attractive - NOT!)
They raise your heart rate - which is extremely dangerous for a number of reasons and also make your heart beat "harder" making the heart enlarge more with each heartbeat, this has long and short term consequences and has in some cases proven fatal to previously young, fit and healthy individuals.
Increases risk of developing diabetes and at a much younger age than you possibly would have without consuming these. There's also some research that shows that acquiring diabetes due to this makes it a harder to manage form of diabetes
Can cause/worsen certain neurological disorders and functioning
Makes you more vulnerable to chemical addiction generally, and this of course is not limited to "street drugs" but also alcohol and prescription meds
Caffeine addiction itself is not to be dismissed, I unwittingly became an addict myself via "just" coffee years ago, I quit "cold turkey" for health reasons and became extremely ill instantly. Thought it was a flu type thing felt absolutely lousy, was vomiting, dizzy, fainting all sorts. Went to gp who correctly dx caffeine addiction and advised I wean myself off gradually which I did.
As for the smoking, well I know teens think they're immortal somewhat you are not. Smoking has long and short term consequences for your health, more than happy to provide MANY examples of patients Young (by which I mean not much older than you now) and older suffering pain, fear and dying due to smoking.
It's not "cool" it's certainly not "glamorous" it's plain stupid in this day and age with all we know to even take up smoking in the first place, I genuinely don't understand it at all, and I have a dd not much older than you (19) and the vast majority of her peers are very critical of the few youngsters they know who smoke (it's certainly a reason why they won't date these people, total turn off) it's definitely not "fashionable" ime for that generation. Even among the few that partake in cannabis tend to not smoke it now but use edibles instead (NOT that I am remotely condoning this either!)
The people I know who are smokers are my parents generation, the younger generations mostly thankfully have more sense.
Especially NOW the LAST thing you need to do is compromising your heart and lung systems.
Particularly as younger people are being generally let down over covid detection and treatment
The only person who can truly ensure your good health is you. Don't let yourself down