What is mares eat oats?

"Mares eat oats" is a popular children's nursery rhyme that dates back to the 19th century. The full rhyme goes:

Mares eat oats And does eat oats And little lambs eat ivy A kid 'll eat ivy too Would you?

The rhyme is often used as a tongue-twister due to its repetitive nature. It is also commonly used as a way to teach children about different animals and the foods they eat. The rhyme was made popular by the singing group The Andrews Sisters in the 1940s.