S.H.
You seem to be doing fine.
Main thing is that he enjoys it.
You might also get workbooks.
Also, have him practice sounding out the letters.
ie: "A" apple, ah, ah, apple. That type of thing.
"B" ball. Buh, buh, ball.
"C" cat, cuh, cuh, cat.
That is what my son's Teacher does in his Kindergarten class at the beginning of the year and in Preschool they did that too.
It is called an alphabet chant.
Sounding out letters, is also important. Phonics.