Children of cancer patients are at risk for developing psychological symptoms. The parental appraisal of the child's psychological condition is a key variable for the utilization of child-centred psychosocial services. This study aimed at the systematic analysis of parental appraisals of changes in the emotional condition or behaviour of their children. We conducted an epidemiologic survey with a sample size of 1,809 patients with different cancer diagnoses, giving information about 2,581 children aged 21 years or younger at time of diagnosis. Quantitative information on children's distress during the disease and on changes in psychological condition or behaviour and qualitative information on the kind of changes were analysed. About half of the children were considered to be psychologically strongly affected during the disease. For about 25 % negative changes in psychological condition or behaviour are reported, positive changes are reported for 20 % of the children. Negative changes are most frequently described in young children (up to five years), positive changes are most frequently described in young adults (18 to 21 years). The results indicate that from the cancer parent's view many children are substantially distressed. Thus, the implementation of additional preventive psychosocial services seems reasonable and necessary.