Myeloid malignancies in children are divided into acute myeloid leukaemia (AML), myelodysplastic syndrome (MDS), juvenile myelomonocytic leukaemia (JMML), and the myeloid leukaemia of Down syndrome (ML-DS). Predisposing genetic conditions are common in MDS. Differentiating MDS from inherited bone marrow failure or AML may be challenging. Therapy consists of observation, immunosuppression, or stem-cell transplantation (SCT). Germline and somatic mutations deregulating the Ras/MAPK signal pathways are key initiating events in JMML. Genetics in JMML defines clinically relevant subgroups and indications for SCT. ML-DS presents with unique clinical characteristics and responds favourably to reduced doses of AML chemotherapy; however, relapse is often refractory to therapy.