This is really a personal decision, rather than a legal one. If you have a child between the ages of 18 and 21, who is a "child attending school" per Oregon law, then they will be a party to the proceeding with regard to child support issues, so that may affect your decision. Minor children are sometimes more deeply involved in the legal process if a custody evaluation takes place. Basically, what I'm saying is that children eventually figure out what's going on so you will want to sit down and talk to them at some point but that's something for you and your spouse to discuss how to do it in a thoughtful, loving manner, rather than something you need legal advice to do.
Good luck with everything.
My responses to posts on AVVO are not legal advice, nor do they create an attorney-client relationship. In order to provide true (and reliable) legal advice, an attorney must be able to ask questions of the person seeking legal advice and to thus gather the appropriate information. In order for an attorney-client relationship to exist, you and I both have to agree the the terms of such an agreement.