(1) being the parent, lawful guardian or someone lawfully charged with the support of a child under 18, born in or out of wedlock, the person knowingly fails to provide support for the child

(2) it's not a defense to a prosecution that either parent has entered into another marriage, that issue has been born of a subsequent marriage, that the defendant is the parent of issue born of a prior marriage or that the child is being supported by another person or agency

(3) It is an affirmative defense to a prosecution under this statute that the defendant has a lawful excuse for not paying child support

(4) If the defendant intends to rely on the affirmative defense in (3) they must give the district attorney written notice of intent at least 30 days prior to trial. The notice must describe the nature of the lawful excuse on which the defendant is relying. If the defendant fails to file notice as required, they may not introduce evidence of a lawful excuse unless the court finds there was just cause for failure to file the notice within the required time

the term issue used in (2) is a technical legal term meaning all of a person's lineal descendants, including their children i.e. it includes grandchildren and so forth.
In this statute it isn't clear if its meaning is just children or also includes descendants as ORS doesn't provide a formal definition. Given the context, it is most likely to mean children.