In chapter sixteen Epictetus encourages us to guard ourselves against believing that another person's loss of child (or material possessions) is 'truly bad'. We should be willing to sympathize with other people when they are grieving, but not with our 'whole heart and soul'. We are to remember that people get upset not by what happens but by their view of what has happened.
I find myself in disagreement with Epictetus here. Even if the pain someone else feels is due to their judgments about a situation, this doesn't make the pain they feel less real. For example, someone might be devastated by loss of a keepsake from their grandmother or grandfather. Even accepting that the keepsake is just a material object doesn't make losing it not painful. Accept in truly childish situations, like if someone was heartbroken over their PlayStation 4 breaking down, I think we should recognize that they are hurting and sympathize with them.
In the case of losing a child, again I think Epictetus goes too far. Although it is impossible for us to guarantee that our children will never experience harm, the loss of a child cannot be dismissed indifferent or placed on the level of losing material possessions. We are not ourselves in a vacuum, but in community. I am not myself in the absence of my family, friends, and larger community; instead, I am only truly myself in the context of my family, friends, and larger community. Of course family and friends are outside of my control, but they are also part of me. So the loss of a child is a loss of part of one's self.
My position on this probably means I am not stoic, at least not all the way up and down. For myself, I think it is possible to genuinely mourn the loss of a loved one and recognize that we cannot keep them from death and harm. I believe that this is healthy, to genuinely mourn and to understand what we can and cannot control, to not repress our feelings but at the same time to keep ourselves from despair.