If my wife signed off at being the beneficiary of my 401k at 20%, allowing my children to receive the balance, is she entitled to receive more with ao

I cannot answer your question without more information, especially as it seems as if your answer was cut off. Off hand, if she signed an agreement (Property Settlement or Marital Agreement) accepting 20% of your 401k that should be all she is entitled to unless she can prove things like fraud, or that you withheld information.