In Massachusetts the custody of a child of unwed parents comes under MGL 209C and is usually determined through a Complaint for Custody, Visitation and Support. If the father's paternity hasn't been established, either through formal acknowledgement, birth certificate, or paternity test, then he has no standing for a claim of custody. If paternity is established, then two issues arise: 1) the child's father will become liable for child-support 2) appropriate custody will be addressed based on the "best interests of the child." The rebuttable presumption will be that where the mother is the primary care-giver - she should remain the custodial parent. The court will, however, try to integrate the father into the child's life - usually through some level of visitation. If, during the proceedings, the mother and father can agree on a custody and visitation agreement, the court will usually accept it and make it the order of the court. It would be unusual for the father to gain any degree of custody of the child other than legal (ex., ability to influence decisions of medical treatment and education), but visitation is a real possibility. The court will consider each parent's ability to contribute to the child's physical, intellectual and emotional development, and the child's health and well-being. The court will also consider the logistics of the custodial arrangement - do the parents communicate well - do the parents live far away from each other - do the parents have suitable living arrangements. I would caution the mother that the more involved the father and/or his family becomes with the child - the stronger his argument for custody becomes. To protect your rights and the best interest o the child, you should confer with legal counsel. Custody actions can take many unexpected turns. This is not legal advice and is not intended to create an attorney-client relationship. You should speak to an attorney for further information.