Aim This paper reports the prevalence and its related sociodemographic factors of informal caregiving by underage children in Austria. The quantity and intensity of caregiving activities, the motivation for and effects of caregiving and how this differs from non-caregiving children were investigated. Background Young carers are a worldwide phenomenon. Due to methodological and sampling problems, little quantitative data are available. Design Cross-sectional, descriptive study. Methods Based on a random selection of 85 schools and 474 classes, a total of 7403 children aged 10-14 years completed a self-reporting questionnaire that asked for children's help in their families. Descriptive and inferential statistics were used to analyse the data. Results In the sample, 4·5% caregiving children were identified. The average age of young carers was 12·5 years. Most young carers were female (69·8% vs. 52·7% in the non-young carers group). Young carers assumed more responsibilities (household tasks, general care and sibling care) than their peers. They showed a higher level of physical (e.g. headache 38·2% vs. 24·4%) and mental (e.g. to worry about 68·1% vs. 41·8%) adverse effects than non-young carers. Extrapolation suggests a rate of 3·5% young carers in underage children of 5–18 years in Austria. Conclusion: Data on national level are essential preconditions to initiate support for young carers. Nurses can promote children's health and well-being through prevention of an inappropriate caregiving role.