There’s a person on my local forum that has been imparting seminars on Blockchain around schools in latam countries. He’s not very active recently, but perhaps he can share some of his experience with you if you PM him.

See:
Blockchain Seminary
Blockchain Seminary #2

Connect with your students on social media for sure that it will be much easier to know who really wants to be your audience. We are the same on the profession but I am not still practicing it as I am in-between if I want to continue it or not. By posting some crypto or blockchain-related content on your social media accounts and if ever there's a growing interest by some of your students on those posts maybe you can encourage them now if they want to dig deep on the technology or not. I advise you to start with just a few participants, stories may spread if it's good or not.

Just a suggestion I guess it will be good if it will not be within the school premises if you teach them why not teach them during weekends. And a fair advise it will be good if you really are that knowledgeable to the technology before teaching them.

As a teacher for secondary school, you don't need to go deep in the technical.

The best guy around to talk about bitcoin and blockchain, in my opinion, is andreas antonopoulos.

He is a very good speaker and writer, he can explains how this works very well, in a way anyone can understand

Check his youtube channel

https://www.youtube.com/channel/UCJWCJCWOxBYSi5DhCieLOLQ

Watch his speeches, and tell what you heard to the kids. Some of them will really like it.

It is nice to see that thing has already started, and it would be nice that you share some info about your progress in work with students. For me it would be very important to teach students about technology which stands behind Bitcoin, and its practical application in today's society. Most people are today intrigued with bitcoin and cryptocurrency in general just because of possible profit.

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Just one more advice regarding posting - you can (and you should use) multi-quote option to reply to other users and not like you did. To do that just pick first post you want to reply and after that scroll down and you will see all posts with Insert Quote option.

Before you even plan to go on that route on teaching kids cryptocurrencies I think a much better approach for this is for you to start lessons about financial planning and investing because diving in to the topic about cryptocurrencies would only leave them with more questions than answers. Just think of it this way, if people the same age as ours are having trouble understanding what cryptocurrencies are what more could the clueless kids understand from your lesson? Just my two cents with your current plan.

Though bitcoin or blockchain technology seems complicated especially to those younger minds, I admire your innovation to integrate this kind of technology and how this bitcoin works. If I were just by your side, I will accompany you to teach those secondary students. But i will just teach those who are willing to learn. It is hard to force them to learn something about new technologies like bitcoin.

However, continue your purpose since the Principal allowed you to do the teachings. Just make it a simple, collect some infographic and videos for them to understand it well.

First of all, it is commendable that you want spend your free time to learn your students something about blockchain and cryptocurrency. But for start, you should pay attention to some things which are very delicate when it comes to such projects.

You say that you ask head/principal to allow few hours for your lecture, and since you work (probably) in state school, everything you do there must be approved by authorities, and parents of students would have to agree with all the extra-curricular activities.

Besides all that you also have to take responsibility for everything that is going to happen after. Some students will probably try to trade, others will try crypto gambling - some will become victims of hacking, and all of them will at the end blame you for that.

I do not say you have to give up on your idea, but you should consider each step well and pick only those students which really show sincere interest for blockchain technology&cryptocurrency.

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Not related to topic, but advice for you - I see you are good in English, but most of your post are only applications for bounty. I suggest you to try participate more in forum discussions, in this way you can also help others.

Check edx.org there are many free courses on blockchain and crypto currencies from leading universities and organizations. There you will find resources and ideas how to structure your classes.
There are other online free courses available in Internet, I just give info based on my own experience.

You will learn a  lot as well.
Good luck!

If ever the principal will allow you, I think you will only do that by just the vacant time of students and it will be only optional for those students who want to attend in your activity if ever the things that you want to teach are within the syllabus/lesson plan you are assigned to that is difficult to pass, but still, that is good initiation.

There's nothing wrong for teaching other people especially on new technologies such as blockchain or Bitcoin.

My advice when you will start teaching young students, you should first identify your listeners/students their knowledge, how you will deliver your lesson to them because I know they will find it difficult at the start and some are don't have an interest. Since you are a teacher I know you already figure it out and have your solution, I know you can manage it