Rationale Previous studies have shown that children may take on higher extents of caring activities if their parents are affected by severe illness or disability, especially when their parents lack access to formal and informal care. Aims and objectives This study examined the extent and nature of caring activities done by patients’ children; differences in caring activities between different types of parental illness; factors associated with caring activities. Design An explorative cross‐sectional multicentre study. Methods Parents as patients in specialised healthcare services, and their children, were recruited from five health trusts in Norway. The sample included 246 children aged 8–17 years and their 238 parents with severe physical illness (neurological disease or cancer) (n = 135), mental illness (n = 75) or substance abuse (n = 28). Main outcome measure Multidimensional Assessment of Caring Activities (MACA‐YC18). Results A large number of children with ill parents are performing various caring activities. Increased caring activities among children due to their parent's illness were confirmed by their parents, especially with regard to personal care. We found no significant differences in the extent of caring activities between illness types, but there were some differences in the nature of these activities. Factors significantly associated with the extent and nature of caring activities were as follows: better social skills and higher external locus of control among the children and poorer physical parental health. Parent's access to home‐based services was limited. Study limitations In recruitment of participants for the study, a sampling bias may have occurred. Conclusion To promote coping and to prevent inappropriate or extensive caring activities among children with ill parents, there is a need for increased access to flexible home‐based services adapted to the type of parental illness.