Bit of trivia: Kiosks are actually the most expensive part of the shopping centre (in a cost per square metre comparison) - because they are prime real estate.
Okay - first things first. There's no way you'll get a commercial retail lease. You're legally not allowed to sign off on it - and commercial premises aren't going to accept your parents signing off for you (on top of which you'll be looking at $1,000+ a week).
Why not start small? You've got a huge advantage in that your target market is right in front of you - at school!
Once you've sold a bit of product and you know it's going to go well, I would then suggest looking at getting a stall at the local markets.
With a bit of creative marketing you could make some decent money this way, and it will cost you very little in overhead ...
Do you do economics or business principles at school? Or similar subjects? Because I would totally recommend having a chat to a teacher who teaches one of these subjects ... they'd be able to point you in the right direction and tell you what you need to think about in terms of taxes, purchasing, business planning and tracking. Having that kind of support will be invaluable.
good luck!