What is a good Christian book that can help the relationship of an unmarried couple with children?

Most Christian churches have a book outlining the marriage ceremony as part of their liturgy. There is no better book than this. Ask your Christian leader to read this to the unmarried couple, and with their appropriate responses, to conclude a marriage. In some countries, it may be necessary for the children to be formally adopted. Having a formal structure to the family will help the relationship of the couple with children.