Interest rates. Pun, very intended. :)

Lend them money, and tell them the rates are volatile, but fixed after they lend you money. Make them determined by "the market". Except, in reality, you adjust rates based on their interest. Get the pun?

I tried to get them to understand self-banking and paying yourself back with interest but that went over like a lead balloon and they got terribly confused and thought that I was explaining simple saving.

Its not a bad idea to introduce lending, but if the loans were priced in bitcoin that could tear them up when the price multiplies several times. Deflation is terrible for holders of debt, wages go down but the loan stays the same.

If I gave them a loan in fiat (an inflationary currency), and let them pay it back over time with their bitcoin (deflationary asset), this could work to their advantage and help them retain their past earnings.

I could also collateralize their loans, so if they default, I can take back their toy and sell it at a discount to their siblings. Devious, but it might work.

I just re-read my own reply. I mixed up the advice in my first 3 words of the advice part. Must have been multi-tasking. Sorry.

Correcting, and clarifying:

Borrow money from them. Post a daily rate that changes, based on their interest in lending you money, but lock it in once the deal is struck for a specific term.

Do it in BTC terms. High interest rates. I'm talking like 200%.

Kids need to see and measure the difference day to day. From their horizon, any fiat is stable.

Presumably you could afford to pay triple digit annual interest for a week or two on on their (assuming small) stack.