If you are going to teach it with the child who is 7 year old, you are going to use the word that can easily understand or comprehend them, but it really depends on the child if the child is not interested they will not easily understand it coz we all know that age is not the age that a child will give time to understand it. There is a child who are very curious but only few.
There are many ways to teach kids about Bitcoin, you can Comparing candy bars like Bitcoin and having money to get them if more money will buy more candy, I think that if the right combination, children will understand very quickly. While many children have been very smart since they were not in school