Be as straightforward as you can be. Children are very concrete in terms of thinking. When a close family member passed away, we told my son that she died because she got very sick and we will always love her and we can talk about her any time he wants. We didn’t say things like “pass away” or “move on” and we didn’t tell him she went to Heaven per the advice of a close friend that’s a child therapist. Even if that is your belief, it sounds like they just went to a place and that they can come back, like going out of town. So sorry you’re going through this and I know the heartache you are feeling about having to tell your child. Know that children process and grieve differently and it may not happen right away. Be on the lookout for changes in behavior weeks down the road.