Paediatric health‐care professionals have a primary duty to promote the best interests of their patients. This is reiterated in article 3 of the United Nations Convention on the Rights of the Child and is predicated on promoting children's health and wellbeing. However, there is ambiguity over what standard applies when evaluating whether a paediatric health‐care decision supports good outcomes. Values like ‘best interests’, ‘doing no harm’ or ‘quality of life’ may be indeterminate or vague and clinicians may have difficulty in conceptualising what exactly constitutes ‘a good life’ for children. This uncertainty leads to the question: how do we best evaluate paediatric health decisions and outcomes? Patient‐reported outcome measures (PROMs) are questionnaires that aim to achieve this by attaining data on a patient's quality of life and wellbeing. While PROMs originated with adult cohorts, they have since been applied to paediatric populations. Children are vulnerable due to their interdependency; and this raises ethical tensions regarding the potential benefits of such data, respect for autonomy and assent/consent of the individual child in clinical settings. These inherent tensions should be balanced by realising a collective good for children. PROMs should be a robust data collection source that facilitates substantive justice, both procedurally and in distributing limited health resources via accurate quality‐adjusted life‐years generation. This article aims to (i) overview the traditional and emerging paediatric PROMs; (ii) outline the tensions of using PROMS for children in a clinical setting and (iii) analyse the ability of traditional and emerging PROMs to promote justice in paediatric resource allocation.