children doesn't need to know about currency,but teenagers does,and i think there's so many explanation video in youtube so don't wasting effort wasting your time when you can just give them about the link of video so they can learn from it,whether they will be interested or not,it's definitely depend on them
I saw different media presentations for kids and teens about bitcoins there are even songs too, just check on youtube because your approach to children should not be that technical when you are trying to explain them about bitcoin because children nowadays tends to lose focus very easily and without it you would just be talking into the thin air gaining nothing.