Teach Your Child to Read in 100 Easy Lessons
I heard about this (Teach Your Child to Read in 100 Easy Lessons) book from my sister who had used it with her children. I used it with my two youngest sons when they were about 3. I remember I was almost in tears, when my middle son read a stop sign. With my youngest, we got through most of it, but it gave him the tools he needed to be a solid reader. He is a bookworm, even now at 16. My sister did use it with her kids at around 2 1/2. Our kids were early talkers so maybe a rule of thumb would be to use as soon as they start developing language skills.
This book worked wonderfully for my boys. One does need to read the parent instruction carefully, I read it more than once to make sure I followed the program (being the stick-to-the rules accountant that I am). The only regret is that I did not have this book to use with my oldest son, he learned to read by 4 but he does not have the same enjoyment of reading as my youngest two.

Janet
St Petersburg, FL