Mine is from when I was 2 years old. I'd woke up in the night and heard my mum crying. I walked to my door which had a safety gate on and my mum was heading down the stairs in floods of tears. I asked her for ju (juice) she said "one minute baby" and went downstairs, reappearing with a sippy cup of water for me and telling me to have my drink and go back to bed. I found out years down the line my dad had physically pushed my mum out of bed and beat her. So it was probably that which woke me in the first place.
I've just asked DS1 his earliest memory. His is being sat at nans house and nan juggling the yellow ball pit balls while he was sat in the ball pit. He'd have been around 18 months old when that happened and I had no idea he even remembered it as we've never spoke about such a, what seemed to us, innocuous incident. I'm so glad his early memory is a happy one though and nothing like mine. He giggled his little head off watching nan juggle especially when she dropped that balls!