If doing what is "right" means I have to hamstring my kid's chances, then I'm going to pass on "right" (or, more likely, re-orient my thinking to make it not "right") and help my kid.
Most societies do demand that workers for important roles be selected on merit or based on other criteria known to all participants, and not based on some individual's wish to care for their family or friends.
This is without anyone thinking of such a wish as illegitimate. However , acting on it is still nepotism and societies impose this prohibition on its members because it benefits all. In this sense, "parents providing for their children" is "losing out" in certain important domains all around the world.
Most societies become pretty practical after a while, and strive for people to be reliable and adequate for the roles they're appointed to play and celebrate the occasional master of some craft or pursuit. Being groomed for an opportunity from childhood, under the attention of one's family, often delivers on those and so a lot of societies don't worry about it except when it's obvious that somebody completely incompetent has ended up responsible for some influential or essential role.
It's actually a very peculiar modern experiment to expect every role to somehow be filled by the most capable person and for every person to be appointed a role that they're personally passionate about. Maybe it'll give us some amazing Star Trek utopia someday, but you don't see that idea expressed very much in history and so we don't really have reason to know what will happen if we try to make it so.
Nowadays I would also guess that the majority of people across the globe live in societies where nepotism is conceived of as bad. There might still be various amounts of it but people generally tend to discourage or punish nepotism when they can.
But there are a bunch of services helping "teach the test" for kids going to college/grad school, and in very, very many ways, middle class (or better off) parents do strive to give their kids tons of advantages that other kids do not have. Is it fair that my kid had access to their own computer and all the books they wanted to read, etc., when others didn't? No, but parents are still going to help their kids.
If we had something resembling a really fair system, kids and adults of any age would be able to take classes and learn whatever, with as much help as they needed. It would be expensive, but fair. That isn't what we have.
But yes, I would argue nepotism is prevalent in nearly all societies.
You can teach them your trade. You can show them that education is important, modelling and rewarding behaviours like reading. You can make sure you've got time to be there for them. You can introduce them to your friends in other lines of work. You can check their homework and help them when they struggle, within reason. You can make sure they never need a part-time job to get by while in school. You can get them tutors whenever they're having trouble. You can get them extra tuition outside school. You can pay for them to go to a great college. You can cover their living expenses when they're working an unpaid internship. You can invest in their startup. You can assure you that even if their startup crashes and burns, you'll make sure they always have a roof over their head and food in their belly. You can buy them a house, pay their bills, gift them millions of dollars.
And you can hire them to work for you - as long as you make a point to clearly not favour them in the workplace, by insisting they work hard every day, don't use your name, and that they start at the bottom and work their way up on their own merits.
And you can overlap these things! In your role as CEO give them an unpaid internship in the mailroom of your company, and in your role as a parent give them a $10,000/month allowance? Technically not nepotism.
The only things you can't do is give them undeserved promotions, or hire them directly into a senior job.
[0] "Harm" doesn't need to be catastrophic. Misuse of company funds is a kind of theft, and paying someone a salary who is basically on perpetual holiday is unjust, for example.
Not every society struggles/struggled so poignantly with the contradiction between those things as we now do, but we do, and that's where the modern criticism of nepotism originates.
Teaching your children your trade by inviting them into your workshop or boardroom is sensible, but it inevitably means that there's less room in that workshop or boardroom for the scrappy, bright outsider whose supposed to have a fair chance.
There's not really one right answer under that kind of tension, so there's no surprise when criticism is levied in either direction.