The “standard” approach to mitigating the harms of single motherhood is to match two or more single mothers up in cohabitation, and divide the responsibilities in some fashion. Remarriage is essentially a second option, on which we would not choose to rely. However, there are many factors, including those that prevent remarriage, that make even this basic social arrangement, a tacit acceptance of slavery. By maintaining this situation, we can consider that many of these governments essentially criminalize any kind of cooperative private arrangement, even beyond parenting; and such, these governments are creating the problems they claim to try to solve.
Housing and domicile restrictions: eviction protections and rent controls force the landlord to keep the tenant. Since these cooperative arrangements exchange rent or similar, this means you don’t get the option to remove a disruptive parent or her kids from the situation (you are poor, you can’t just go rent another place). So, once you let another family in, you’re stuck with them.
Criminal accusations: naturally all of the evidence-free convictions, combined with intimate quarters, mean that if the other parent decides to accuse you of misconduct, or get her kids to do it, you will go to prison whenever she feels like it. Even if there is due process, and you are eventually found innocent, that’s not going to stop your employer from firing you, and putting you and your children out on the street.
Income cliffs and similar welfare state aberrations of households: combining households means now you have to report the same to the various welfare authorities, who then e.g. based on whether you are sharing meals (which is rational given the whole point is to be more efficient and save money), may reduce your benefits.