What is the earliest possible age to start teaching children how to play chess? My daughter is 4 years old, and she plays checkers very well for her age. She asked me if she can learn how to play chess too. So I am interested in what is the best age to start teaching her. Is it too early to do this?  Does anyone have any experience?
Depending on several factors, the age to start teaching a child to play chess can vary.

The mere fact that she asked you how she can play chess is a good sign that she is interested in learning.  Interest is one of the key factors because we don't want to force-feed them the game.  If I had to pick an age, I would say 4 is a good age, but it depends also on maturity.  I would also say not to expect too much and let her have fun. A great place to start is http://wwww.chesskid.com

My 2 (almost 3 year old) stumbled upon Chessmaster by accident.  He was more intrigued by the movie type intro to the game rather than the actual game itself, nevertheless, he remained interested and knows all the names of the pieces, but that is about it.  He knows that it is a game, but if I tell him something like "Take the knight", he will take a pawn on some square and go all the way across the board and take it, lol, so based on my own experience, 3 seems to be too young in most cases.  I have really yet to see 4, but when my kid reaches 4, I guess I will find out, but based upon his reaction now, I think he would have a good grasp of the rules by age 4, maybe earlier.  As for now, I just let him have fun.