Marginalised children are uniquely vulnerable within western societies. Conducting participatory design research with them comes with particular ethical challenges, some of which we illustrate in this paper. Through several examples across two different partic-ipatory design projects (one with autistic children, another with visually impaired children), we reflect on the often overlooked tensions on the level of micro-ethics. We argue we are often required to rely on multiple moral frames of references. We discuss issues that the immediate interaction between researchers and marginalised children in participatory projects can bring and offer an understanding of how micro-ethics manifest in these collaborations. We contribute to a theoretical exploration of ethical encounters based on empirical grounds, which can guide other researchers in their participatory endeavours.