Well, on a positive note, my baby can read. He turned 4 last week and , given he's spent most of the afternoon reading about the battle of britain in the RAF museum, not just 3-4 letter words, I'd say that qualifies me to give an opinion 
On the less positive side, (For you), it's not something (IMHO) you can teach a child of that age (even less that you would WANT to). They either want to do it or they don't. And if they do, you don't need to worry about any fancy flash cards for them.
On the less positive side (For me), my son's ability to read is almost certainly at the expense of his ability to socially engage with children of his own age. So, while learning about the battle of britain in some length, he was unable to answer the question 'what's your name?' asked by a similar aged child.
Not sure if that's what you want to hear (I'd guess not) but you cannot and shouldn't force a child to do something they are not ready to do.