Prior to their relationship a mother and father have their own independent lives – their own beds, bank accounts, circles of friends, etc. Most often, as their relationship grows they move in with one another, combine finances, make all major decisions together and with having children even more so bringing them together. Once the decision is made to separate one parent (usually the father) moves out and they have to determine where the children will be and when. At this point this is a separated family.
There are times when both know and agree that they must go their own ways. In these situations there can be some degree of relief, perhaps even affection and love, and the parents work out where the children will be and when on their own.
There are times when there are major disagreements about who should have the children and when, as well as the other practical aspects of bringing children up such as their medical care, their education and how they will be supported financially. The more contentious this is the more likely that the parents will need outside intervention to work it out. There are private, public, religious, governmental, legal and court systems that can assist parents in making the transition into a separated family.