My three-year-old son spends several hours each day on the computer playing educational games. Is there any harm in letting him spend so much time on the computer? He can now read beginner books like Go Dog Go and can easily sound out and name words that I spell for him -- even words he has not heard before. Since he seems to learn so much this way, I have a hard time telling him to stay off the computer.
It is great that your son enjoys the computer and is learning to read. These skills will serve him well in school. Nevertheless, you should limit his time on the computer. The valuable lessons that he needs to be learning now come from active play with toys, real objects, and friends -- not from a computer. For example, through play your young son will discover that ice is cold, wood floats in water, and stacks of blocks fall down if they are not balanced correctly. He'll also learn how to cooperate and share with other children.
Don't let your son spend so much time on the computer that it becomes his major play activity. He should be playing with toy cars, blocks, and dress-up clothes. He should be pretending to be a pilot or a cook. He should be learning how to play alone and with others. He should also be talking and playing with you. And he should be playing outside, too, learning about flowers and rocks and bugs.
You need to understand that kindergarten teachers are not expecting children to be able to read on the day they start school. What teachers want is children who are ready to learn to read, count, and write through the development of solid intellectual, social, emotional, and physical skills. Too much time on the computer could limit your son's development of these skills.
You can learn a lot more about the importance of play in the development of young children by visiting the National Association for the Education of Young Children website.