My earliest clear memory is that of my 4th birthday, from the moment I woke up to a couple of hours later. I remember my mom telling me to get dressed up so we can go to the daycare and after to school, which I started to do and then thought “what’s school? what’s daycare?” (these I asked) “why are you my mom?” (this one I didn’t for some reason). After being fully dressed, we got into the car and drove to the daycare, I was guided to a room that’s next to the kitchen and told to wait. A couple of minutes later, I notice a light coming from the hallway connecting to the kitchen (“what’s that? why is it coming closer?”), then the nanny, her husband and my mom come out with a cake. I then immediately asked why there was a cake, I was told it’s my birthday, and then I asked what’s a birthday.
So yeah I think kids ask a lot of questions the moment or around when they start to be self-aware.
I read some random theory on the Internet years ago that said we may well have memories from earlier, but because of how much the brain changes during development they could basically be encoded in a different file format than what the brain at a later stage of development knows how to decode. No idea where I came across that, or if it was supported by any science or was just a shower thought, but interesting to think about.