Why is it that children grow up with anger, resentment and hate?
They have no idea about the world.

Here are two reasons:
1) they copy the behavior of their parents and/or
2) they are not allowed to be who they truly are, which equals to murdering their spirits. Is that upsetting enough?

As a child you should be given a chance  to truly sense that you have body, that that body is a big part of who you are. In stead of being considered a pawn in the game of the parent you should be related to as to your own person, even while being raised and educated. You should be made clear that you have the right to be your own person for the mere fact that you are living.

That is the way to reduce hate and anger in children and consequently in our future grown ups, and consequently in the next generation as well. By encouraging kids to be their own person you eliminate both reasons for resentment: boys and girls do not have to suppress themselves any more as they are  acknowledged as the unique and independent person they are plus they do not have to copy their parents (traditional, familiar but obsolete) thoughts and behavior any longer as they  learn to think with their own (fresh) mind . This way the world is renewed and the old Romeo and Juliet family/tribe quarrels do not survive.