Naruto's childhood was filled with loneliness but it shouldn't be as bad as it's hyped up to be.
Sasuke's childhood did suck, but since Kishimoto doesn't know how to write human beings it results in teenage angst...rather than insanity, suicidal tendencies, narcissism, traits associated with terrible events like what happened to the Uchiha clan. Sasuke's reaction to getting his whole clan slaughtered? Shrug it off and just keep my mouth shut and be rude to everyone cause I have better skills than everyone else, so I can align myself with the forces of evil even though I could get just as powerful training under Konoha teachers as I would under Orochimaru (and in the long run, Konoha teachers are better cause look at how fucking hax Naruto is.) Makes perfect sense.
Gaara's childhood I don't really buy too much either. But the character arc between him and Naruto was solid so I'm generally ok with it.
It wouldn't be a major issue if Naruto was a comedy series that tries to insert realism. Naruto is the inverse, it's a series where Kishimoto specifically writes everything to be as realistic as possible when it comes to how characters interact with each other and the storylines themselves with some comedy inserted there sometimes. This is why I'm so hard on series like Naruto and Bleach, yet I'm ok if One Piece fucks up. Naruto and Bleach are two series made to be taken as seriously as possible, while One Piece is mainly formatted like a gag manga like Dragonball but has serious edges that happens more rarely than they do in Naruto and Bleach. This makes a lot of the more exaggerative leaps in One Piece a lot more believable to me, cause the whole manga itself is exaggerative. In Naruto and Bleach, you have "real" moments like characters tragically dying or getting traumatized somehow, but it's so badly written and poorly developed outside of some cases that it might as well not be there in the first place.
Also the amount of filler chapters in Naruto and Bleach is insufferable. So much so you can literally read volumes worth of material of Bleach, for example, and be done with them in about 5 minutes when it should take you an hour or thirty minutes to read the average volume of manga (unless you're an ungodly fast reader like I used to be). Naruto does something even worse: It adds dialogue. So much dialogue that there's sometimes important plot progression in the midst of filler material so you pretty much HAVE to read everything to make sure you know what's going on outside of the constant slow lingering of characters chatting about stuff like how great Naruto, Kakashi, Sasuke, whatever are. And Bleach and Naruto are both guilty of this: Training arcs. Issue isn't the concept itself, but rather the fact that there's so many of them and they serve the same exact purpose of explaining shit that no one gives a shit about. Imagine if you were reading a Superman comic and all of a sudden Superman is being told by Martian Manhunter WHY he can fly in large bubbles of dialogue that take up half of the issue of the comic you're reading. That's what Naruto and Bleach does, and honestly who gives a shit?