Mastocytoses are a group of rare diseases characterized, in most cases, by a benign proliferation and accumulation of mast cells in different tissues. In children, mastocytosis affects usually exclusively the skin and differs in many aspects from adult-onset mastocytosis. Except for diffuse cutaneous mastocytosis, which is an uncommon subtype of childhood-onset mastocytosis, involvement of the bone marrow or additional extracutaneous organs is rarely seen in children. The prognosis of childhood-onset mastocytosis is usually very good. Compared to adult patients who most commonly experience chronic-stable or slowly progressive disease, mastocytosis in children is mostly transient and self-limiting. In this review, we present and discuss the subtypes of childhood-onset mastocytosis, recent advances in the understanding of their pathogenesis as well as similarities and differences between adult- and childhood-onset mastocytosis.