Reunion lets you assign a child status to each child button. A status could be something such as Adopted, Stillborn, Foster, Illegitimate, Out of Wedlock, etc. Each child status has its own unique color which appears around the selected child button, giving you a distinct visual clue as you click through the family file.
To create or change a child status definition, choose Options -> Define -> Child Status. This opens the Child Status window, shown below.