My earliest memories have been triggered by seeing a familiar place or home video. Earliest one is probably when I was 2 or 3, playing with my Grandpa in the front yard of the house I lived in til I was 4. That was triggered two summers ago when we visited CA and my mom drove by our old house.
Second wasn't really triggered by anything, but I've always remembered soon after my Grandpa died (when I was around 2 or 3), I was at his old house and there was another old man there (not sure who he was), but I thought he was my grandpa, so I said "Hi Grandpa!" Then my mom talked to me alone and told me he died. It's weird, because nowadays I don't remember being sad or even what my grandpa was like, but as a 2 year old I guess I really liked him.
Another when I was three, my mom had just bought me a new pajama gown that I loved, and I was looking at it in our huge mirror. My dad walked in, my mom told him she was pregnant, and he got upset. I suppose he was just stressed about it.