I think a good plan would be to teach them how to use Bitcoin, how to store private keys, etc.

Then, every year you do a "wallet recovery day", which you should do as a fun thing, kinda like a treasure hunt. Basically you giving them some play money using instructions to recover a wallet that you setup with some sats in there, just so that they get used to the idea.

Every year you use a new wallet with a new seed/private key so that they have to repeat the process to get the sats.

When you pass away, the real wallet will be there instead. You will have to somehow make that happen, but I think it shouldn't be too hard.

Would be nice to self host something like this: https://finalmessage.io/

Still searching for a self hosted free version

Shamir Secret Sharing is the best solution for this.

You generate seed phrases that only work when the minimum threshold is met.

Generate four shares and set a threshold of two shares to recovery the funds.

Keep two in a safe place, that only you know about. Third with a laywer and the fourth in a safety deposit box that your significant other (or family) can access.

On your passing the lawyer releases the third share, your partner combines the share from the safety deposit box and the funds are recovered.

It's also a strategy for disaster recovery.

I hope by the time I have to worry about it someone will have figured out how to do it on a commercial way.

Whoever finds a way to make a business out of bitcoin inheritance will make a lot of money. Perhaps banks will adapt to offer such service in the future?

Also, can you imagine: "here is the qr code with the seed to the bitcoin wallet your father left you". You scan it and it's a link to the youtube video of Never Gonna Give You Up. :)

There are some really involved plans that can get made with multisigs. Here's a scenario/an idea for a movie:

Imagine if you have two estranged sons who don't get along. You havent been able to get them to talk in decades. You create a multisig and hide it in bank safe deposit boxes in towns that are significant to the sons by being places that they had wonderful memories of getting along when they were younger. They have to work together to obtain the keys to get the inheritance and remember how important they are to eachother. You pass along your bitcoin and achieve your dying wish.

The project I'm using is called Safe Haven with their Inheriti solution. The project has different product/ services but the one's I'm using is Inheriti and SafeSwap. You can check them out on Twitter for more details. I hope this helps.

pre-sign a time-locked transaction, give transaction to kids, before time-lock expires invalidate transaction (if still alive)

I thought about this and came to the conclusion that it is impossible to give your coins after death without trusting someone other than yourself.

You are either:

kids should have instructions in a will and the will should also signify a guardian who will take care of them if both parents die