That's a tough one, because some earliest memories only exist because it's been recorded and I've seen it, and because it's me it's sort of become part of a memory? I'd have to say it would be a of first time going to preschool and doing the entry tests to get into reception (pre-year 1 classes R1 and R2 iirc.).

Bonus memory of me telling my mum I wasn't feeling well in the morning before school, and her just chalking it up to me trying to get a day off. Then during registration, sat on the floor, I barf up lol.