We should teach them at the second stage because at that stage they can buy chocolates snacks and even rum errands, to make them understand that there is a digital currency known as bitcoin,this will help them know quick about bitcoin in other to join the moving train when it is the right time for them. I heard a boy of 15 that his father has 7 btc and the boy was the next of kin to these bitcoin. Lack of proper knowledge on btc made him gave out one btc to someone.
We can give them hints on the second stage but I still think the third stage is the best for Bitcoin focus learning.
I do think bitcoin is a bit too complex to be taught well at the second stage. I learnt a lot whe.i was about 13 but couldn't handle things like the number systems until much later (I did an advanced physics course when I was 17 and students were still having issues with that too so that could still be too young unless you've got a good way to teach them).
As a child I think I first learned about money by observation. When I went with my mom or grandma to the store or market, I used to be curious how a piece of paper could be used to get some meat or fish. That's probably the earliest time I learned what money actually is. And then there were also those moments when relatives give you money to buy something. Those were the earliest financial encounters I had. And then later on I wanted to buy some stuff which I had to save for first. That's financial management.
But you have probably relied on parents and teachers/educators to learn how to learn? If you're trying to teach someone something it's sometimes good to get near your limits of knowledge (especially if they're engaging with it and asking questions) and then allow them to grow from there. This might be a bit selfish though as it means they'll probably bring interesting facts of things you don't know and may find interesting or start to ask for help determining whether something is factual.