There is no law or duty to disclose that information, but I would recommend that you let them know so neither party has to dig and search to complete payment of the benefit when you are no longer around.
Also, always remember that a contract (like a life ins policy) trumps a will. If you leave all to all kids equally in the will but have life ins to one child, the life ins proceeds go to the one child with no duty to share.
I agree with my colleagues. I wonder if you worry that the beneficiary might try to expedite your demise.
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