Why do we call it a nuclear family? Apparently it has to do with being composed of a small number of fundamental building blocks.
Every human has had a biological mother and father with the exceptions of Adam, Eve, Jesus, and clones. I'm going to leave clones for another time. You probably have heard the same explanations for Adam, Eve, and Jesus as I have.
Whatever it is that makes us human, was designed by God. Once the prototypes were completed, ongoing production was assured. Father and mother have children. Children become fathers and mothers. Generation upon generation. Along the way uncles, aunts, grandfathers, and grandmothers and a host of other relations came into being. When biological moms or dads can't carry on their roles, others pitch in as needed.
Barbara and I have been blessed with a nuclear family that has only been altered each time we conceived another child. We have good reason to think that the alterations are now complete. The members of our family shift their positions on this globe. Our love for one another grows and matures as does each one of us. Our nuclear family remains composed of the same six persons. There will be a day when death may separate us for a season. After that, we hope to be rejoined for all eternity.
Our relationship with God is central to our being. Our relationship to our family is fundamental to our humanity. I thank God for our nuclear family. I thank God for the joy we have known. I thank him for helping us through the sorrows and for strengthening us to deal with difficulties.