You need to make sure that your key is on media that can be stored long-term. If you keep it on a thumb drive and the drive gets fried, you might as well have had the stuff stolen from you. Also, if you use any kind of password protection, you should put the password in a safe location. If you die in a car crash, it doesn't matter if you will states that your kids get your bitcoin if the only place your password was is in your head.
Your best bet is keeping a password protected private key, including a print-out of it, in a secure location, and keeping the password in a different secure location. And if your intent is to have your bitcoin go to multiple heirs, you should go ahead and create separate keys for each heir. Or set up some kind of smart contract that would split up your bitcoin upon your death.