Your take on "children of God" strikes me as classic mysticism. Christian mystics use similar language. I've always found such language moving for several reasons, not the least being its reliance on analogies, such as your wave to ocean metaphor.
My tradition tends to speak of the matter in one of two ways.
First, you do not have to look long to find Christians who believe the phrase has to do with heaven and judgment. They believe the status is conferred by God, and that it is received in a final judgment. Those who take this view rely on the passive construction of the phrase ("shall be called"), noting that it suggests the title is something given as the gift of God. Some who hold this view, then go on to interpret "blessed are the peacemakers" to mean "blessed are those who share the gospel and lead others to acknowledge Jesus as their savior, and so help others find peace with God." In short, the beatitude is interpreted as a call to practice evangelism. I find this approach reductionist at best, a distortion of Jesus' intent at worst.
A second, and to my mind better, approach draws on an analogy based on the family. I have a son and daughter. Both were conceived and born as my children. Nothing can change their essential status. On the other hand, each has spent well over two decades becoming himself and herself, while remaining my child.
Along the way, they picked up many of my values and some of my practices. We often tease one another gently. With reference to one of their own beliefs, ideas, approaches to challenge, or actions toward others, either of them is apt to say, "Well, I guess that proves I'm your child."
Oceans and waves, fathers (and mothers) and their children--both analogies help us remember who we already are and what we might best do with ourselves. Both preserve our unity with God and our uniqueness. Taken seriously, each conditions us for the work of peace making.