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.
I do not understand that what is the need of teaching a 7 year old about bitcoins. By the time he will reach 20-25 and start earning, bitcoin might have disappeared.
The main reason why bitcoin should be teach to the children is that in this age children got very sharp mind they can easily get whatever you will teach them. Even child expert says the age of 7 is he age when children can learn more than 7 languages, so in short if you will teach them bitcoin at this time they will easily get your concept of bitcoin and in future will be able to invest or use bitcoin to earn money. So they will be able to afford their own expenses so teach them and tell them the easy way of getting money through bitcoin,