All the branches and leaves are children. Document trees are usually visually represented as a hierarchal chart . The most important thing to remember about a structured document is that it is defined by the elements it contains, not by how it looks. Structure says that an element is a paragraph. Format says to display the paragraph in 12 point Times.
Structure says the element is a book title.
Format says to display the book title in green bold body text. Structure say the element is a social security number. Format says to hide and not display the social security number.