Quoting The Doctor:" I think being there for them is the best thing you can do, hun, but also let them know to be honest with ... [snip!] ... want space. Maybe cook them a few meals that are easily reheated so they don't have to worry about that when they get home?"
The hardest time is coming in which they go home without their child. They will have to put up baby items and try to live normally and that will be impossible for a long period of time.
They will need you to most when they are home. Offer to cook meals, help straighten up, or just be there and watch tv with them.
I'm so sorry for their loss.