At preschool age, a good learning game has big targets, no time pressure and no reading required. Everything on this page fits that bar: a grown-up may need to read a word or two aloud, but the tapping, matching and giggling belong entirely to your three or four year old.
Sessions this age should be short and end while they are still fun. Five minutes of letters, a matching game, done. The repetition that builds letter and number knowledge comes from coming back tomorrow, not from pushing on today.