When a baby dies, there are often children in the wider family or whanau, whether they are siblings, cousins, friends or neighbours. And those children will also be grieving - in their own way, particular to their age group and their relationship to the baby or child. Here are some links to information and books about children's grief that may be helpful:
Skylight is a NZ organisation that supports children, young people, and their whānau to navigate through tough times. You can request a support pack from them - they'll send you information and resources specific to your child's experience. And they have resources you can purchase directly - books on grief and loss and the NZ book for children aged 3-7 years about baby loss - What's Happened to Baby?
For example - "a preschooler finds it hard to understand the permanence of death. This age group has rich 'magical thinking' where they may think the person can become alive again or that they did something to make the person die. Preschoolers have a very literal understanding and think in a very concrete way. It is important to use real words such as 'dead'. Euphemisms such as 'lost' or 'passed away' may cause misunderstanding and confusion."
Supporting a preschooler might include:
honestly explain death as a part of life using what they can see (use plants or insects as examples of death in nature)
read children's books together about death and grief
use words that describe feelings
encourage creative play and exercise as an outlet for thoughts and feelings
Here's another article (from the US) on children and grief and how you can help them.
Here's an article from Kids Helpline in Australia that has everything simply presented in bullet-point form.
And finally, an article from a psychologist in 'Psychology Today' on "How to Help Children Cope with Death and Grief". He suggests approaching the topic gently, with truth and compassion.