If I asked parents what is the number one thing they want for their children, I bet most of them would say happiness. Some may have a roundabout way of saying it, for example they may say they want them to have a nice career or a spouse and kids, but that's because they think those achievements will lead to happiness. Either way you can boil it down to parents want their kids to have a happy and fulfilling life.
Despite the fact that this is their goal, a lot of parents end up failing at helping their kids attain happiness. Why is that? Well I think for most cases the answer is simple: the parents aren't happy themselves. This is a classic case of the blind leading the blind.
If you can't figure out how to be happy how the hell can you figure out how to make another human happy? You know yourself better than your kid after all.
Children can tell if you are not happy, and so they know where your guidance will lead to if they follow it - it will lead to your life. So if you don't seem happy the rational thing to do is to not listen to you. I believe this is why kids become rebellious when they grow up. You simply don't have valid authority. They know that you are bullshitting when you promise them a great life if only they do what you say, and you'd be surprised how young they catch on.
I know that true happiness is hard to attain, especially if you don't have guidance from happy people. I don't yet have an answer for how to attain it for myself except that it has a lot to do with freedom. I also know about what doesn't work and one of those things is letting myself be controlled by, let alone listen to people that aren't happy themselves, whether they be my parents, school teachers or society as a whole.
I think it is crucial for any aspiring parent to find the answer for themselves before a child shows up. That is if they want said child to be happy.