The purpose of Parent & Child OKRs is to link Objectives to each other, based on scope of the Objective.
Suppose that "Improve Application Performance" is a corporate OKR (parent), then "Minimize Bugs" is a team OKR (child).
That is, a certain chain is built between Two objectives - the larger objective is the parent OKR, and the smaller objective is the child.
To link objectives, go to "OKRs" and click on the objective you want to make the parent.
Inside the objective page, under "Subgoals," you can find the "Create child OKR" box. To link the objective, click the plus sign.
Here you have an option to select an existing OKR, or create a new objective. In this article, we take a look at selecting an existing OKR. Information on creating a new target can be found in the previous article (see "How to create an OKR?").
Once you click on "Select existing OKR", you need to simply choose any OKR from the list.