How do I select parents and children together in the outliner? So for example I have a model chair which includes the arms, piston (that type of chair), base etc. How do I select all parts including the parent item for duplicating the model? Shift+G only allows me to select the children but not parent. I'm fairly beginner with Blender.

Thanks
Hold CTRL while selecting the parent in the outliner, you should see every children of that object highlithed in orange as well, that tells you they are selected too.