My children were taught by the letter, and by singing it. it makes it easier for them to remember. Sounds come after they know the alphabet. So once they get the A-Z they then start to learn the sounding.

Also with writing, I do think they are a little too young, and you'll have more luck teaching them the alphabet. But if you want to teach them start of with 1/2 letters and let them get those ones, then build it up. One on one time where you can sit down and show them how its done and get them to copy will help. As will the books Ang talks about.