For parents and caregivers who want to support a child in resolving a difficult experience including grief, I've offered simple talk tools relative to your child's developmental age.
A note: In the case of death or trauma that is especially violent or has very directly affected the child's experience of safety, professional support from a psychotherapist is the first step. If you are looking for a children's therapist, research the different types of Play Therapy as well as EMDR on the web. These are the top three treatment modalities for children who are navigating trauma.
Story Telling. Very young children will often tell the story of the event over and over. It can feel instinctive to a caregiver to re-direct the child, but really the child's insistence on recounting the story is their effort to make peace with it. If you find your child re-telling a story over and over, encourage the child gently each time the story comes up. Help them fill in the pieces that they are missing. When children tell stories of trauma they will generally leave out the portion of the story that describes the resolution and return to safety occurs. Validate any expression of fear, sadness or other emotions and gently remind them how the experience ended (eg; & then I came and got you, picked you up and gave you a kiss). Emphasizing deep breaths will help the child regulate their nervous system while they recount the events. When we go through these type of events, our nervous system gets aroused because of the flight or fight response process. Relaxing after we are aroused to fight or flight is easier when we move. For these reasons, you may find it helpful to get a child moving after recounting the story. Running, wrestling, sand boxes, blowing bubbles, art, and most play will help the child re-regulate and calm down. Eventually, the child will either just stop telling the story or they will include an ending in their narrative on their own, that allows them to make peace with the event.
Discussion and Support. At around 7 or 8 years old children begin to discuss events in an organized and accurate way relative to the our adult world. Do not force a discussion at any age, but do bring it up. Your willingness to take the first step can be very important. If your child is not open to talking to you, tell them that it is really best when something this difficult happens that they figure out how to talk about it. This might mean brain storming about who they want to talk about it with, maybe a grandparent or trusted family friend or a professional. Whoever they talk to will do best to have activity planned that will allow for conversation but also busy hands. Again, this will help the child's nervous system stay calm while they go through the process of organizing the events of their story. The conversation itself should cover the sequence of events. Sometimes children (and all people) make up events for parts of an event that they are unsure of. Often the parts they make up are more frightening than the real story. Once the story is recounted, to the relative comfort level of the child, ask directly what they think will help them feel safe moving forward. Check in again in a few months.
Consider the extent to which you are affected by the trauma as well. It is rare that something of significance happens to our children that doesn't affect us at least as much as it affects the child. This means that it may not be as upsetting to your child than as it is you, but still some level of inquiry is probably best. Parents and caregivers need to take care of themselves too. Attempting to help a child relax and let go of events that continue to rock your world isn't effective. The talk tools described for children could be translated to adults as well.
As always, if you feel as though you are in over your head, or your child's behavior and discussions make it clear that they are still struggling, or you feel stuck and overwhelmed, find a professional. There are some really wonderful folks out there ready to support you and your child in navigating grief.