The Collaborative International Dictionary of English v.0.48:

Monday's Child \Mon"day's Child\ (m[u^]n"d[=a]z ch[imac]ld`), n.
   A child who is fair of face; -- a reference to a nineteenth
   century poem. See below.
   [PJC]

         Monday's child is fair of face,
         Tuesday's child is full of grace,
         Wednesday's child is full of woe,
         Thursday's child has far to go,
         Friday's child is loving and giving,
         Saturday's child works hard for a living,
         But the child who is born on the Sabbath day,
         Is lucky and happy and good and gay.
   [PJC]