What happens to a beneficiary designation if the beneficiary dies - is there any protection for the beneficiary's children?

Generally the language in the will directs how the estate will be distributed provided that the will was carefully drafted by a competent attorney. A gift to a deceased beneficiary may pass to her/his heirs, her/his siblings or may lapse and pass into the residuary of the estate to be shared by all the other beneficiaries. The testator has the power to decide while the will is being drafted. If the testator has died you should have the will reviewed by an attorney to determine who receives the share of a beneficiary who predeceased the testator. If the will has been filed for probate then speak to the attorney who is handling the estate.