As I get older, I find that I remember less of my childhood. It's probably normal, and it doesn't bother me too much. (Or it could be a result of Cabernet Sauvignon. If I was drinking bad wine it would bother me. But I'm not, so it doesn't.)
But my earliest memory has been the same for a while: I'm 4 or 5 years old and running around a screened-in porch wearing Mickey Mouse ears while the Mouseketeers were on the TV and my mom was cooking something in the kitchen where my baby sister was sitting in a high chair. I guess this memory persists because all the senses are involved: smells from the cooking, sounds from the TV, movement, sight... That must have been 1959, I guess, since imdb.com says the show only ran from 1955 to 1959. So for me, life on this planet began 47 years ago.
So, what's your earliest memory?