Oops forgot to reply to the original thoughts.
IF children show an interest I pursue it. Usually at around 4ish. But it's always in a casual fun way. If we're playing outside I'll take sticks and make a letter, or draw one in the sand. If we're playing inside I find ways to do the same with materials we're playing with. I'm not a teacher. If they want to learn then great, we'll find ways to do it with fun and play at the same times so they'll start to recognize. If they ask, I'll give them markers and help. I'm here as an introduction, let's make circles, let's make lines, look you can make a balloon by putting those 2 together. Three straight lines make an A and that starts your name.