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.
It can be a good idea to share your knowledge about bitcoin but sharing it to a 7 year old child is much difficult to do, although in that old child can think but its mind is focusing on playing and curiousity about its environment so you are right to explain it in much easier way like using some words that easy to understand.