The fact that the disease sequelae can limit the development of the growing child’s activity is the feature of pediatric medical rehabilitation, that is why there is a need for repeated courses of rehabilitation or habilitation, where each subsequent course is a continuation of the previous one. The specialist’s mission is to determine indications for rehabilitation. The paper reports phenomenology and methods to diagnose abnormal activity and participation in convalescent children after infectious diseases in order to set the rehabilitation goals in the International Classification of Functioning, Disability and Health domains (categories). The use of method to estimate activity and participation from the point of view of both child and parent or caregiver is considered. The paper provides information useful for specialists dealing with the issues of rehabilitation of children after infectious diseases.