What is the legal term for a cohabiting partner who has children but is not married?

The term "cohabitant" accurately describes a cohabiting partner who may have children but is not married. This term broadly encompasses individuals living together in a long-term relationship that resembles marriage, but without the formal legal status of being married. Cohabitants can have various legal rights and responsibilities, particularly in terms of parenting and shared assets, depending on the laws of their jurisdiction.

Other options like "common law partner" may refer to couples who are recognized as married without a formal ceremony, usually after meeting specific criteria that differ by location. "Legal partner" and "Partner In Will" do not specifically convey the idea of cohabiting individuals who are not married and could also lead to confusion regarding their legal rights. Hence, "cohabitant" is the most precise term for the context provided in the question.