Can a husband change his life insurance policy to include his new wife in the state of Washington if it is stipulated in the dissolution that the children are to be the sole beneficiary of the policy?

If the husband is the policy "owner", and the children are listed as "revocable" beneficiaries, then the change can be made. However, you can be sure [that] when the husband dies, the new beneficiary designation will be challenged. Think carefully about this before you act. Perhaps , assuming the husband is insurable, a new (additional) policy should be purchased naming the new wife as the primary beneficiary.