Bestselling author and literary consultant Mem Fox states in her book Reading Magic that "rhymers will be readers". Based on research by experts in literacy and child development, she claims that children who know eight nursery rhymes by heart by the time they are four years old will be among the best readers by the time they are eight years old.
Childhood experts say that nursery rhymes can help stimulate your child's memory, improve their language skills and develop their appreciation for music. Parents and children have liked them for centuries without the PhD's approval because they are fun.
Here is a link to a nice Nursery Rhyme site.