I am trying to figure out how to pass on bitcoins via trust or will or some other service/instrument.

The problems are multiple

[1] How do you trust some one to do this, they can simply abscond, and it would be hard to track/stop/recover

[2] If the child/beneficiary is not technically good, and can't grasp private keys, and the pitfalls with bitcoin use, and wallets, encryption/duplication and back up of data sets etc

[3] Air gaping etc

I'm sorta thinking that you need a service, that gets one key file for say true a crypt container and another separate organization gets another key file  and both then sends them to the beneficiary and neither organization knows who you gave the other key file to.

then the person can unlock the encrypted file, which you left them on multiple media and cloud etc, and you have to leave detailed instructions and say some GLD coins or cheap coin in a wallet/with private keys as well and tell them to play with that first, back up etc etc

open to ideas

It sorta really important say you get hit by a bus , and don't have this set up, that's its all for nothing.