I've read The Free Child: A Libertarian Guide to Raising Independent, Self Confident Children by Frances Kendall

One of the things this book mentions, is that your child is basically just a very inexperienced person. This is not entirely true as my book about the human brain points out (there are many parts of the brain that grow in different rates that cause children to act very differently than adults), but to speak in a short amount of words its true enough to be useful.

Remember that kids are not generally "set in their ways". They are way easier to teach than adults. Simply setting up a testnet wallet for them will typically be enough to show them how to use Bitcoin.

https://padawanwallet.com/ The above link is a very nice testnet wallet that goes over the basics of using Bitcoin.

https://blixtwallet.github.io/ Blixt wallet not only has an interactive demo on their website, but they also have a testnet version of their application.

mempool.space does actually allow you to see your testnet transaction in the testnet mempool. https://mempool.space/testnet

When they're ready, you could pay their allowance in Bitcoin, show them the online stores (https://www.lightningnetworkstores.com/) and it may even be fun to have a small store of your own that accepts Bitcoin.

Last but not least, there are plenty of other posts on SN where people express their experience talking about Bitcoin with their children and I implore you to read those as well.