Which comes first - writing music or reading music?

Writing music comes first for children starting at age 4.  If a children writes a symbol that represents a sound, the child can "read:" what he or she has written.  Reading what someone else has written is far more difficult for the child, even though it is certainly possible for some children.
Around age 4, the hand of the child is physically ready to write, to leave a mark, to express his or her own thoughts.  Writing is a simpler process than reading, because the sound to be written is known to the writer.  Reading, however, is more complex since it involves the analysis of each graphic symbol into its unique sound.  The act of decoding (reading) is a translation of someone else's thoughts, which represent an unknown, whereas writing language is self-expression - recognizable by the writer (or the child who wrote it).  I like to have 4 year olds draw their own notes for the sounds we know so well.  We begin with Sol, Mi, and Do, starting at the top of the page and descending to the middle, and then to the bottom.    This prepares them for the act of decoding musical notation at the appropriate time!   (source: Musikgarten/Music Matters)