The 40 substantive rights contained within the United Nations Convention on the Rights of the Child (UNCRC) 1989, have applied, without discrimination, to all children in the United Kingdom since 1992. However, recurrent tragedies starkly highlight the potential vulnerability of some children when their parents experience mental health difficulties; and many children affected by parental mental illness remain a hidden population, the unique challenges they face going unaddressed. Article 3 of the UNCRC states: "All organisations concerned with children should work towards what is best for each child". Social workers occupy a critical position in safeguarding the UN Convention rights of children, particularly in situations where mental illness is having an adverse impact on parenting, and where children are "in need" or "at risk". However, collaboration between Mental Health and Family & Child Care services can be problematic. Poorly-integrated service provision constrained by inadequate resources and training, and complicated by a latent dichotomy between the human rights of parents and the Convention rights of children, can contribute to regrettable outcomes for these most vulnerable families. This article highlights the potential psychological vulnerability of children living in a situation where one or both parents experience mental health difficulties. Evidence regarding the scale and impact of parental mental health difficulties is explored, and discussed in the context of the UNCRC, and the key findings of recent Child Protection Inspections and Health & Social Care inquiries in Northern Ireland. The article draws on relevant literature (specifically the Western and Eastern Health and Social Services Boards Inquiry into the tragic deaths of Madeleine and Lauren O'Neill in Northern Ireland, and the preliminary findings of research being carried out by the authors within the University of Ulster) to illustrate and consider the problems associated with social work practice with these families. The article concludes by making recommendations to enhance effective, responsive, collaborative social care provision for children in families experiencing parental mental health difficulties. (Contains 1 table and 1 note.)