Possible Clues:

• Preschool song ender
• ''Old McDonald'' refrain
• Refrain consisting of vowels
• What might come after a cow or a sheep?
• Letters sung as mi, mi, re, re, do
• Letters after 'had a farm'
• '' . . . had a farm, __''
• ''Old MacDonald'' ending
• Vowels sung to children
• Mi-mi-re-re-do, in a children's song