...taken from Wikipedia...
Though uncertain, the traits assigned to each given day probably parallel traits assigned to planets, the Sun, the Moon represented by various Gods in Norse, Roman, and Greek mythology. For example, the English word Friday stems from the Norse goddess of Love, hence the notion that children born on Fridays will become 'loving and giving.' In addition, the word for Friday in many Romance languages is derived from the word 'Venus', the Roman goddess of love and beauty; other days of the week follow accordingly. There is also the likelihood an ancient rhyme had evolved over time and lines were reassigned to different days for cultural reasons, as in the case with the final rhyme for the Sabbath day being identified for Sunday instead of actual Judeo-Christian biblical scripture identifying Saturday as the Sabbath. In fact, a strict historical review of the rhyme would more correctly have the verse read:
Sunday's child is full of grace. (Christian day of worship)
Monday's child is fair of face. (Mon=Moon, with its 'face')
Tuesday's child is full of woe. (Tues=Týr, Norse 'God of War')
Wednesday's child has far to go. (Wednes=Woden 'The Wanderer')Thursday's child works hard for a living, (Thur=Thor, Norse god)
Friday's child is loving and giving. (Frida=Freyja, Norse 'God of Love')But the child that is born on Sabbath-day (Saturday=Sabbath)
Is bonny and happy and wise and gay.
Adam Fox ("Oral and Literate Culture in England 1500-1700" p182) quotes the Elizabethan Thomas Nashe. Nashe recalled stories told to "yong folks" around a fire which included "tell[ing] what luck eurie one should haue by the day of the weeke he was borne on". Nashe thus provides evidence for fortune telling rhymes of this type circulating in Suffolk in the 1570s.