I sat my 7yr old son down and showed him my ledger nano and how to use it in case anything ever happens to me.
I explained there is electronic money on it and it will be his one day. Went through the process of wiping it and restoring with the seed. But reminded him never ever tell anyone about it is our secret.
He's a smart kid and was amazed at how it's secured by an extremely complex code and that no one can steal the money you can take it anywhere and it's safer than a bank because the ledger is a bank itself (i know that's not quite correct but still). I didn't tell him how much are on there but told him one day it will be extremely valuable that's why I'm telling him about it is for him when he grows up.
Later that day we talked about how to secure the seed and printing it on a metal plate. He thinks it is so cool.
It amazed me how a child instantly understood it and showed how cryptos are for the future generations not us. We are early adopters so buy at least 1 bitcoin for your kids. Just might set them up for life.
It would be a very good move educating your child about cryptocurrency but I don't think that its a very smart move telling your child about your private keys since as we all know 7 years old is not that mature enough to understand how important private keys are. It depends on every child though but most of them are not really good in keeping secrets since most of the children are always telling the truth and they can be persuaded by adults to disclose your private keys buy giving them something that they really want and that interests them like things, toys, food or anything that they are fond of. Atleast tell them when they are already in their teens or atleast 18 years old or just disclose your private keys to your wife or another member of the family that you trust the most.