There are several "gospels" not included in the canon; a google search of non-canonical gospels will yield a plethora of information on them. While the canonized gospels are considered trustworthy and their authors are considered to be who they say they are, other gospels don't look to have the same reliability (at least that was my takeaway when I researched the topic for a paper several years ago). There are books about Jesus' childhood but they're kind of goofy (Jesus using magical powers and whatnot, as if that wouldn't give him a bunch of attention) and made me think that the author was making it up as he went. As for why there are no authentic accounts in the NT, I'd guess it's because either those with first-hand accounts didn't write anything or because Jesus stayed under the radar until He formally began ministry and as such, accounts of everyday life weren't necessary.