How to move the parent object to a child of one of its children?

I want a parent Game Object to parent itself to one of its children. How do I do this?

Can you explain in more depth? A parent GameObject is already a parent of it’s children.
Do you want the parent to become a child of it’s children?

If you know exactly what GameObject you want to set as the parent (Make your current parent a child of) then you can just use a reference of it.

Transform child; //Set the child object
transform.SetParent(child); //Set this transform to be a child of that object.

If you’re unsure what child specifically… It becomes a much harder problem. If you have a way to identify it however, you could later use:

Transform child = GameObject.Find("Object Name").transform;

String finds are messy though, I’d recommend something a little more deterministic.