He quickly grew out of it as his language developed further and I believe similar cases are just young kids being unable to express their ideas accurately.
However, your hypothesis is very compelling.
Context about developing self-awareness (from some random site): https://www.fatherly.com/health/children-five-stages-self-aw...
To be sure, the article discusses two year olds and I neither remember being two nor and I suggesting that my imagination when I was young somehow explains away these accounts.
Nonetheless, as I say, wild times for a child mind trying to "form", trying to figure out how to process the world.
I recall some nightmare that would return periodically over a span of years. Or maybe not? Like deja vu, the mind is an unreliable narrator.
The night terrors I am quite sure were real. They finally passed sometime in my teen years. Sadly I had to witness night terrors in a few of my own children. Thankfully for them I knew what they were and would stay up and comfort them in the night until they fell asleep to forget. And I could tell them that these too would pass.
So while still being the skeptic of anything like reincarnation since it would upend the world view I have carefully pieced together from almost sixty years of observation, I did recognize in the children that untamed mind I once had when I was their age.
And this part: “Scientists say consciousness is produced by the brain…” - there is no other side to that position. There’s nothing else there.
(Yes, I would say the same to a kid about life after death too.)
I guess Native American reincarnation works and eastern variants do not