The oldest of my children is 4 years old. She can't interpret digital numbers very well yet, so we use dirty fiat coins. If they want something I subjectively don't like, they have to pay for the item themselves. They get their pocket money in coins so far too.

When their grandparents give them some money, I deposit it in bitcoin and keep the books for them.

As soon as they are interested in using mobile, I would like to switch to bitcoin. With the understanding that I'll be their exchange agent if they need it. It will then be up to them how much of the funds they keep in fiat and how much in bitcoin (bitcoin will be the default choice)

When I have time, I'm considering using a paywall on services like YouTube. For example, I'll buy premium so they don't watch stupid ads, but they'll have to stream sats for every second they watch..