Every mother has a responsibility to tell their children as much truth as possible. Reasonably telling the child the truth about their father can be difficult but will help the child put things into perspective. 

In this story, the mom was trying to do what she thought was best, protecting her son from the truth about his father. As the story went on, the son became more and more troubled with the lack of clarity. He was so troubled, it even entered into his dreams. Experiences like this can result in a lifetime of emotional consequences. Keeping facts like a father's death from a child, as seen here, can be traumatic. 

When the truth is presented at the right time, the child is posed to learn to make healthier emotion decisions about who they are, rather than live in emotional strife wondering "where's Daddy?"