Repetition helps teach small children vocabulary, so songs like "Old MacDonald Had A Farm" are great for teaching animal names and their associated sounds. There's a similar song I learned in West Virginia:

I had a cat and the cat pleased me, and I fed my cat under yonder tree. The cat said Fiddle-I-Fee.

You add a different animal with every verse and repeat the ones which went before, always ending with the cat, such as:

I had a cow and the cow pleased me, and I fed my cow under yonder tree. The cow said Moo, Moo; the pig said Oink, Oink; the sheep said Baa Baa; the horse said Neigh Neigh; the dog said Woof Woof; the cat said Fiddle-I-Fee.