Tl, dr: KHR would be very rich land to dig up generational pressure, burden of legacy and family trauma.
Anyways, onto the point of parents/adults in KHR and chilren.
First and foremost: yes, it is adults’ responsibility to protect kids. Totally agree.
The thing about adults’ protection in general (this can be apply to any environment, not just mafia) is that it would come down to this one fatal flaw: They think they know best.
In KHR it spreads to many, many other flaw but really all flaws of adults here roots in the same way, they think they know best and what they do is right.
And in KHR there are two other flaws that specifically in the mafia setting: 1) some too value of legacy and 2) they are mafia by core, so as a results, their kind spirit also is hence shaped by their life until it is like a flickering flame itself and thus only can be spent to light a very small number of people that they care about.
In some ways, no you can’t say “the adults do not protect the kids”. The adults here protect the kids a lot. HOWEVER, 1) their definition of protection is their own version of thinking “what is the best protection” and they do not care if that aligns with what the kids want; 2) they only do protecrion to a very limited target. Iemitsu protects Tsuna by not letting him know anything about his job, and with the Flood of Blood incident as well as Enma’s family as the parallel, Tsuna growing up very peacefully is considered his success. Nono protects Tsuna by telling Dino to test Gokudera and ready to eliminate him in cases he fails the test, rising from the worry Gokudera is too wild animal that can hurt Tsuna back. Iemitsu protects Tsuna by making a deal with Mukuro so Tsuna has enough guardians for the Ring Battle. Lavinia protects Gokudera by not telling him the truth about her so he will never got too heartbroken by her about to pass away.
The adults here do protect the kids but they do not care if the kids want that kind of protection or not, because adults think they know best. And their heart is only limited to a very specific target, not encompassing all of them. Which is why this both opposite statements stand, as the adults protect the kids but also at the same time, harms the kids. Because some kids are simply not on their radar of protection. Iemitsu doesn't care for Lambo and others when making them as Tsuna's guardians. Nono doesn't care for Gokudera when testing him to make sure Tsuna is safe. And so on.
So far, we do not have any proofs to say that they are wrong. Tsuna grows up peacefully with his mother until he can’t. Tsuna has a strong guardian that later be one of his strongest friends and ally. Gokudera also grows up peacefully despite being a literal bastard until he misheard the truth. So far, all the protection here has a succesful outcome as intended purpose.
So far, we also have many proofs to say the adults make thing terribe. Tsuna grows up peacefully at the cost of him doesn’t have any preparation for the bomb dropped at his head, having no one reliable to talk as he has a big case of miscommunication with his dad, which add another factor in why he grows up to be such a kluzt. He has a strong guardian but at the same time he will not need a guardian if in the beginning he doesn’t get thrushed into all this mafia mess. And in the end Gokudera grows up not knowing the fact that he got loved so much, and now the period when he is a street kid, being rejected multiple times and so alone will never be erased.
We can’t even say “If the adults do it different, thing can be better”. Who gonna guarantee if Iemitsu tells his family about his job, they will not end up being killed as his subordinates in Flood of Blood, Enma’s family, Nono’s three sons, and many other family got involved in mafia in general of KHR world? Who will make sure Tsuna would not protect against having Mukuro being his guardian if Iemitsu tells him about it first time? And we never know if it would be better if Gokudera knows the truth about his identity as a bastard and his true mother only has a few months or days to die.
We can’t even tell adult Tsuna to “do it different” because if he does not toss teens and kids into battlefield by kidnapping them, world would doom and all would die.
And well, finally, the legacy. Which is why this is funny to me because to me (and I say with proof) so many adults do terrible thing just for the continue of legacy. Nono wants to continue Vongola so he turns to Tsuna as the last resort without caring if he wants it or not (and even when Tsuna rejects it, he shrugs “It’s fine” then process to tell Tsuna “If you don’t want to be Decimo, how about Neo Primo as title?” which basically just boss title makeover). Iemitsu wants to keep Tsuna away from mafia, yet eventually submits to the legacy and pass the agree that Tsuna will be a candidate for Vongola boss title. This is such an endless suffering of cycle because as long as they belong to a “family”, it is eventually will become their fate to find themselves chain to the responsibility of continuing it. Tsuna hates mafia with passion, and he even says he wants to destroy Vongola. But, as the Future arc shows us, even though it is only a possibility of what Tsuna can become, it shows us very well that in order to keep Vongola standing (which has now become his family) Adult!Tsuna is willing do inflict the same treatment as what his adult figures in life has done to inflict sufferings on him. The very same treatment of staying silent to his own family while doing thing at their back and not care one damn about what the kids feel. Because he needs this family to live on and his family is now Vongola.
Side note, the Simon family is also a case how legacy doom all of them. They technically can just be a civillian and live on. But no, Enma hates the boss title but he still has to stand up as a boss of a family that may very well be dead long ago. Other kids, especially in Kaoru and Rauji’s case who likes Yamamoto and Lambo a lot, when standing in front of the duty of legacy aka fight as Simon’s guardian, they do not hestitate to ready to kill the person they just called friends.
If anything, all children and parents here are some sort of victim to that legacy, and the older victims aka adults do what they thing is right to shape the younger victim aka kid to adapt to the situation. “Getting stronger”, “getting friends” (which are downright hardcore mafia) all the good shounen typicall mottos are just cover for a method of adaptation so that one can survive in the mafia.
And lastly it is so funny to me because none put up this. KHR could dig this up and cook it live how Iemitsu’s parenting is both right and wrong at the same time because both sides have it very own parallel. He keeps his son safe by not telling him anything and does not let Tsuna involve in mafia. The first paralle for it is Xanxus: being keeps silent about the truth, desvastating when find it out, and process to wage a civil war that none can make excuse for his tantrum. The second parallel is Enma, who knows about his family’s true business as mafia, and then witnessing his own family got murdered right in front of his eyes. Heck, they can even bring Nono’s three sons onto a table of how both knowing and involving in the business will not end up happily but nope.