Skin eruptions sometimes appear as the first signs of disease in children, allowing for early diagnosis and treatment. Examination of the child’s skin is a routine element of the physical examination, which provides valuable information facilitating the correct diagnosis. Distinguishing individual skin eruptions that make up the overall picture of the disease often causes diagnostic difficulties in the context of rash diseases in children in the practice of a primary care physician. These diseases include viral, bacterial, and parasitic infections as well as those of ambiguous aetiology, such as Kawasaki disease. In this paper, individual primary and secondary skin eruptions are characterised. Primary eruptions are typically a direct result of the development of the disease process in the skin; secondary eruptions, in turn, usually develop from primary eruptions, as consequences thereof. A rash is a lesion that affects the appearance and texture of the skin surface. This paper discusses the most common infectious diseases with a rash in the clinical picture. In addition, when differentiating infectious rash diseases in children, attention was paid to other – non-infectious – skin diseases, such as atopic dermatitis, seborrhoeic dermatitis, and psoriasis. These are disease entities characterised by a diverse clinical picture depending on the stage of the disease and the age of the child. When diagnosing a high-fever child, life-threatening conditions such as meningococcal sepsis, with petechiae that do not disappear under pressure, should always be considered. Prolonged fever, especially lasting more than 5 days, should prompt the physician to conduct diagnostics towards Kawasaki syndrome – a disease of ambiguous aetiology.