The truth is, universalists, unitarians and other theological liberals will have to try to dig up other biblical texts than Malachi 2:10 to try to make this patently unbiblical case that all people simply by virtue of their physical birth are somehow children of God, united with Father God. Being created by God does not automatically make everyone his spiritual children.
No, we are not all children of God:
On a surface reading this verse does not appear to be all that problematic. But as with many passages in this series, it is the way it is so readily misused and abused by many others that causes the problem. The verse in question says this: “Have we not all one Father? Has not one God created us?”
The misuse of this text comes about when cultists and heretics try to make the case that we are all not only God’s children by physical creation, but we are all also his children in a spiritual sense as well. Universalism is one of the names of this particular heresy – the idea that we are all saved, that there is no hell and final judgment, and that we are all doing just fine with God. See more on this theological error here: billmuehlenberg.com/2011/03/12/against-universalism/
There are several challenges that we can bring to bear in dealing with such a faulty understanding of this verse in particular and the whole of Scripture in general. The first thing to say is this understanding is only partly right. And that is how cults and heresies usually flourish: by using part of the truth, and twisting it as well.
We ARE all God’s children in the obvious sense that God created every single one of us. We all exist because God made us. So in that sense, sure, everyone is a child of God. But Scripture also uses this notion of being a child of God in a different sense – a different spiritual and theological sense.
That is, only those who are in a right relationship with God are seen to be children of God. This is clear from all of Scripture. Ancient Israel as a whole was seen as being part of God’s family, but not the surrounding pagan nations. And in the New Testament only those who come to Christ in faith and repentance are regarded as being a child of God.
Jesus made this crystal clear when he rebuked the religious leaders of the day who were clearly NOT in right relationship with God. He called them children of the devil (see the whole exchange in Matthew 25:31-46). That is the condition of everyone unless they make a deliberate turn away from sin and turn to God. But all this I discuss in much more detail elsewhere: billmuehlenberg.com/2016/01/13/no-we-are-not-all-gods-children/
The second obvious thing to say about this erroneous interpretation of this text is this: as always, context is king. Simply reading this verse in light of its immediate context makes it clear that there is no universalistic mush being promoted here.