A study examines the prevalence of problems in children within four months after a parent's cancer diagnosis (T1) and six (T2) and twelve months (T3) afterwards. Sixty-nine ill parents and 57 spouses completed the Child Behavior Checklist for 57 primary school (aged 4-11 years) and 66 adolescent children (aged 12-18 years). Adolescents completed the self-report version. Children's functioning was compared to that of the norm group and a sample of families that were confronted with parental cancer between one to five years before study participation (retrospective study). Most children were reported as having a similar level as or fewer problems than was reported in the norm and retrospective studies. Reported problems decreased with time, but children who initially had more problems remained vulnerable during the year. Fathers and mothers highly agree in their perception of children's behavior, with the exception of adolescent daughters' behavior. Agreement between mothers and adolescent daughters was high, whereas agreement between fathers and adolescent sons and daughters, and mothers and adolescent sons was low to moderate. The outcomes suggest that most children do not experience problems shortly after the parent's diagnosis and were functioning over time on a level equal to or better than that of their peers. Differences in informant's perceptions appear and remain of interest.