Are prenup agreements legal and enforceable in Washington State?

I’m engaged to be married and my fiancé and I live in Seattle. We have discussed entering into a prenup because we have both been married before and want to protect assets we have already acquired during those relationships. We also want to preserve our estates for our respective adult children. However, the research I have done on the internet suggests that Washington disfavors prenups and may not enforce them. Is that true? If not, what do we need to do to ensure that any prenup we enter into is legal in this state. Is there a test the court performs to determine whether to enforce a prenuptial?