I do not know if this will work with earlier versions of Unity, please comment if your version does or does not work. To keep Parent/Child objects together and make placement easier, instead of creating an object by using the GameObject tab, Right click on your parent object and select your new game object. This will automatically make that object a child of the parent and place it in the same place of the parent. This is a great tip especially when you have multiple objects all over the place.
You can also make a child to a child object. Say you made a booster with a cone on top. If you made the cone a child of the booster then when you duplicate or move the booster it will move the cone with it as well.
