With all due respect, the scriptures are clear that we are not all children of God. Only those who God has adopted into His family are children of God. The scriptures teaches that the rest are children of wrath-children who's father is the devil. And just so that Christians don't get a big head, since we must be adopted into God's family, then it follows that Christians at one time were children of wrath as well. (Eph 2). Evil exist in this world because most of the world are children of wrath and do the will of their father.
As far as "bickering and fighting" among Christians, the only reason this occurs is because it is evidence of 1) our sinful state, and 2) tares or false doctrine within the church. The first problem is indeed ourselves that fails to conform to the image of Christ. The second is where Christians alt to speak out and failure to do so is the sin of omission. And there's the paradox for a Christian; knowing when to speak and when to remain silence. But if we fail to warn a brother that, say, Mormonism is wrong, then then sin remains on our heads. If we have done so, then we just might help someone.
Apparently many are willfully ignoring my point here. The point is not what I believe or don’t believe, the point is that we all have much more in common than we think and we must all work together to defeat evil and turn our country around.