The problem seemed to solve itself when he turned three. Now, Billy is four. This is where our story ends, until tomorrow. Teach your child the alphabet. Teach your child how to rhyme, as well.
Children learn to rhyme very quickly and love to make up nonsense rhymes.
Encourage your child to do so. Visit your library. Take your child to story hours. Most public libraries have a story hour for young children. Today, many bookstores do, as well.