Common language that you see on bank accounts and/or brokerage accounts is “joint tenancy with right of survivorship” or “pay on death.” Both are ways to create assets not subject to probate.
If you have a will that says, “I leave everything to my two children equally”, but you deposit all your savings in a certificate of deposit, for instance, which is in your name and in the name of one of your children as “joint tenants with right of survivorship”, then that child will be presumed to be entitled to everything in the account. You will have no assets to pass under the probate of your will. Your other child will receive nothing.
If you fail to carefully attend to this detail, your failure can cause a lot of strife and hard feelings in your family after you are gone.
(The above should not be construed as specific legal advice and is intended for general information purposes only)