It's a great thing that you are discussing it with your kid and I am sure with these efforts, he will feel much confident and familiar in the coming decades as we are heading towards decentralized era.
seed and printing it on a metal plate.
However, I would advice you thinking again in this regard because it is not recommended to make even a single digital copy of seed key. You never know which program might pull it from your computer. Precaution is better than cure, don't you think so?