If you are going to teach it to the child who is 7 years 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 is very curious but only few.
But if I think 7-year-olds are too early to teach Bitcoin. I know age does not preclude learning Bitcoin. But should the child of that age let him enjoy first periods of play with his friends?