You just said a will can be written, WILL contains everything you have, properties, money and so on, if money can be included why not Bitcoin? Anything can be WILL to your offspring.
Yeah, anything can be WILL to your offspring, but adding bitcoin demands that you have a certain degree of trust and understanding with the lawyer managing your WILL
Your bitcoin assets are under the jurisdiction of anyone who knows your bitcoin wallet's seed phrase. Anytime he wants, he may exchange it.
What I would do if I were to include bitcoin to the WILL of my offspring, is to purchase a hardware wallet, give it to the lawyer, and give my children access to the hardware wallet's password. My children should meet the lawyer whenever I am no longer alive because I will specify in the WILL how the bitcoin in the hardware wallet is to be shared
That's probably a good way to go about it. No one in the world can be trusted these days, even the closest people to you can deceive you any time when it comes to money because money is everything for everyone these days. So if you don't trust your lawyer, which you shouldn't, you should simply buy a hardware wallet, store the Bitcoins in it, give the wallet to the lawyer, and give the password to the children to keep it somewhere safe as it's important.
Also, tell your children that your lawyer has something with the will which is a device that you guys should get when I'm no more and that device can be unlocked with the password given to you earlier. Any other detail that you want them to know which isn't confidential should be written in the will.