Didn't discover MBTI til 15 or 16. But here is a bit about me as a child.
I was a shy and introverted child, but I was quite smart, and I could form proper sentences... I can't remember, but my mother said it was very early. I was definitely N as a child. I paid little attention to the external world and got in trouble because I was absent minded. I had very specialised areas of expertise, mainly dinosaurs at first, and in grade 1 I could spell palaeontology speaking. I also liked writing stories, and was pretty good at it. I made 1 friend in pre primary who I played with ALL the time and nobody else. He left the next year. I slowly made some other aquaintances but could not name many of my classmates. About grade 3 I became a total loner and spent breaks walking around thhinking and singing a song from the Jungle book. I was also failing class because I kept wandering off on trains of thought. I had no taste in music. I just listened to what my parents did mostly. I was diagnosed with ADHD (primarily innatentive) and was given medication for it for about a year. I got a bit better at paying attention and made a friend, but not that good of one. They sort of just admired my drawing skills. I was EXTREMELY gulligble as a child and believed everything I was told. I believed another student could teach me magic and followed him around like a sheep for a whole term. Around this time I started worrying what other people thought, which was not a good thing. I became jealous when others beat me at stuff I liked and began craving attention. I (somehow) became a class clown around year 6, and I could be a bit rude and immature. My areas of expertise shifted but I was still focused on whatever they were, not paying attention to the world as a whole. I also developed a small but close group of friends, including a tomboyish girl who would have a crush on me at age 12, though I was still very nervous about sexuality and rejected the very notion. Also, I became less humorous and less popular, just becoming some weird kid, but I didn't mind because I had a good group of friends. I became a bit more cynical and rational though and got annoyed at the social heirachy system in which at my school, a jerk was the most popular kid, and he was slightly better than me in computing (one of my areas of expertise) and was constantly called as the computer expert despite the fact I wanted to help.
And that concludes my primary school life and my evolution of character up to age 13. I'd say I was INTX (like now) for most of my life, though I had a period where I leaned towards E, which I did not like later.