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.
Firs off, would it really be necessary to teach a 7-year-old about the principles of bitcoin. I think it's too early to do so. Also, it won't be as useful to them, especially in this stage where it is not really of the mainstream market. Having said, in response to the topic, I think first talk about where you could closely compare it to like money and what you can do with it. Because, if you would start with the concept then I'm sure any seven year old would hardly be interested.