The Fukushima Daiichi Nuclear Power Plant accident (hereafter referred to as the “nuclear accident”) caused radiation anxiety among the population. Various organizations have conducted surveys on radiation anxiety after the nuclear accident, but studies on children have been limited. The purpose of this study was to obtain information on the differences in the factors contributing to radiation anxiety among parents and children who lived in the areas affected by the radiation disasters and their changes over time. The results showed that parents were most anxious at the beginning of the nuclear accident with a decreasing trend thereafter, whereas their children showed multiple patterns, including 1) little anxiety from the beginning, 2) anxiety at the beginning but decreasing early on, and 3) more anxiety in later years than at the beginning. For parents, the main factors contributing to anxiety were feelings about their children and confusion about information received. For the children, the main factors were increased knowledge and changes in their lives. This study suggests that the perception of radiation varies greatly even between parents and children living together.