Say you are sorry. Admit your own helplessness and frustration. Cry if you feel like it. Encourage siblings to express as much grief as they are feeling. Allow parents to express anger.
Anger is healthy.
Recognize a parent's need to talk about the child they have lost as much and as often as they want, or to review the circumstances of the death as often as they like. Encourage parents to talk openly about their feelings, but don't push. Everyone's needs and desires are different. Be sure the kindness, you plan is acceptable beforehand by confirming it with parents. Give specific examples of what you can do and what you can offer.