Children develop interest in learning ABCs (and many other things) at different times. Simple rhyming books are a great way for your child to learn about letters and sounds. Once your child begins to show an interest in written letters, teach them the letters in their name. Make games and art projects involving the letters of the alphabet. If you follow your child's lead in determining when to start, you can make learning the ABCs or any other school-readiness skill fun and interesting.
Unfortunately, today’s parents often teach their children the ABC too early. An experience preschool teacher – who’s been teaching preschool for 30 years – told me that children should not be taught the ABC until they start kindergarten. Children should learn the ABC in their natural environment – from street signs, books, while they’re in stores, at the mall, in the library, etc. Parents can point out the letters and their sounds and introduce the English alphabets to their children. However, if parents feel compel to teach their children the ABC, it should be taught “out of order” and not in alphabetically order.
Its good to see that you are interested in your child's education. When you are considering "teaching the ABCs", are you concerned with naming the letters, attaching the sound to the letters, or writing the letters? Each skill can develop at different ages. For example, writing a letter with a diagonal is easier at 4 1/2 years than at three because the perceptual development of a diagonal is present. This can be seen when a child builds with blocks using diagonal placement of a block at this age.
Ames and Ilg have wonderful books based on each year of a child's life that explains the developmental milestones in great detail. They could be of great help as you encourage your child's development!