Like some others have mentioned, I think the conversation for Bitcoin is one that should definitely wait until a child has a basic to moderate financial literacy. They should understand the US dollar (or whatever currency is used in their country) and mechanics about that currency before they are taught about Bitcoin, or the concepts of blockchain and cryptocurrencies as a whole. Maybe one day Bitcoin will stand on its own as a worldwide recognized currency with an established value in people's heads. But right now when people think of the value of Bitcoin, they put it into terms of how much of their country's currency (or USD) it is worth.
For example: if someone said: "This car costs 1 Bitcoin", then the question to follow would most certainly be: "How much is that in dollars?", so that you can get an understanding of what the car is worth in relation to what you've seen other cars valued at, all in USD.

I came across this video talking about this dude who made a game to teach kids about Bitcoin: https://youtube.com/shorts/j85ITb3Cnoc?feature=share