This is a two part question, I suppose. Jesus of Nazareth is widely regarded to have existed as a human, correct? All of the bible was written by those surrounding him or anticipating a messiah. Why is there no personal accounts or teachings by him? And do the missing books of the Bible leave any more information about his adolescence?
So, the Gospels were not written contemporaneously with the events described within. They were written somewhere between thirty and seventy years after the events described (all of which took place around 30-33 AD ish). For those years between 30ish AD and 65-100 AD, teachings were conveyed through oral tradition as well as through other documents. There are just tons of these documents, and they're all different kinds from apocalyptic writing to prophecy to different church teachings.
But the important part is, the Bible wasn't written when Jesus was around. Jesus was a preacher and that's how he gave his messages.There are lots of famous people who could have given their memoirs or their opinions in their own words, but didn't. He's one of them.
There is a hypothetical Source called the 'Q Source' Which comes from the Two Source hypothesis It basically comes from the idea that the Gospels of Matthew and Luke used an independent source that isn't the Gospel of Mark. This Source would have been an important text or Oral tradition regarding the teachings of Jesus.
However It's existence is brought into question by scholars due to a lack of evidence
I know that Wikipedia is frowned upon here, however I think that it makes a nice summery. however be wary of misinformation as anyone can edit.
In regards to the second part of your question. I would check out the Infancy Gospels. Not biblical canon but tell stories of Jesus's youth. Infancy Gospel of James and Thomas
He couldn't couldn't read or write and neither could his followers.
He was also preaching an apocalyptic message. He thought the Messianic age was about to happen in the near future. He wouldn't have seen any reason to preserve anything because he thought the world was about to end, or at least change drastically.
In addition to the Gospels not being written simultaneously with the events protrayed, it is important to also keep in mind the literary context of the time. While the Gospels are named after disciples, that doesn't mean they were written by them. It was common practice in that time frame to write something and attribute it to someone else; today we call this plagiarism or forgery; it was actually quite common at the time and known as Pseudepigraphy. So while the books of Matthew and Luke sound like they were written by Matthew and Luke, we actually have no idea who wrote them. They were titled that in order to get people to read them.
The non-canonical Infancy Gospel of Thomas is a text that has stories of Jesus's adolescence.