It is not necessary to teach kids about digital currencies even bitcoin, I mean let them experience the word without knowing this kind of things. Learning digital currencies means that they will be learning a lot especially in the side of the economy making their lives more serious and take their freedom as a innocent child. Let them know it in their own ways, we do not need to force them even if it is giving us good profit.
We don't actually force them to learn bitcoin, we just make sure that we get their interest in this kind of market. What I mean is that, let them observe you while doing the transactions. Children learn so fast nowadays, especially that we are already in the digital era. If it happens that bitcoin will be mandatory to use in the next coming years, your knowledge in bitcoin will be the kids of next generation's edge. Just explain about it to them little by little. No need to search for ways to teach it to them.