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.