: Despite the marked improvement in overall survival rates of paediatric patients with haematological malignancies that has been achieved during the last decades, there is still a pressing need for novel therapeutic approaches for the subset of patients with relapsed or refractory disease. Immune checkpoint inhibitors aim to induce potent anti-tumour immune responses by targeted blocking of inhibitory receptors and have shown promising results in preclinical models and studies on the adult population. However, paediatric malignancies present unique features, and so far, experience with these agents is limited. In the current review, we present an overview of efficacy and safety data from case reports, case series, and clinical trials employing the use of immune checkpoint inhibitors in children, adolescents, and young adults with haematological malignancies. We also discuss new possibilities involving novel targets and combination treatments and provide a summary of the currently registered clinical trials.