There are different reasons for which children become anxious and fearful. They also express their uncertainty, insecurity, worries, fear - or in other words anxiety, in many different ways.
Even if it is impossible to address whatever causes the child’s uncertainty, insecurity or worries, it means a lot to a person when the anxiety provoking things are acknowledged. This is the least what can be done.
If it is possible, the children need to be patiently shown how to manage their fears - very practically. We as adults have come up with many ways of successfully dealing with worries and fears as we experienced a lot of them by now...Pass them on to the younger generation.