If you have a few children, you could try using multisig, but then there's that one of your children dies after you, but before they can share the money. You could also use a time lock, but then, it doesn't mean you'll time it well enough. You're 50 and you have a 10 year old child, so you lock your coins for another 5 years, but you're still alive, so you keep going, finally you lock it again and die a year later, so your child will have to wait 4 years? That's pretty harsh.
I'd put the instructions and seeds in a capsule and hide it somewhere. I'd give the location to someone that I trust, but make it hard for them to break into it. Let's say you have children and you tell them where the capsule is, but it's under a concrete floor in your living room, so they'd have to use an electric tool and need a whole day to uncover it. They won't do it wile you're alive, but should have no problems getting to it when you're gone.
I've actually thought about this subject before now but your approach is really nice. The only problem with this method is the person you would leave the information of the seed phrase to, as he/she might claim the funds. What about generating and giving the different private keys to the children, so that they can come together and access the funds when the owner is no more? The problem with my suggestion is if the children does not have the fear of God they can even spend the funds while the owner is still alive.
Physical note book like you said is not bad but have you considered the durability of the note book? Can it stay for a long time without being damaged? Is it possible to protect the content for a long time against others that do have access to your house?
It's always advisable to keep your seed phrase safe from a place that's far from water, fire or any sort of damage but if you are scared of using a note book, you can engrave your seed phrase on a metallic steel.