Hi Jen, First of all I'm so sorry to hear about the death of your sister's mother in law. For the children to witness that, is just terrible. I feel that at their age, they are too young, especially because of what they witnessed. They can't process the sight of a dead person in a casket. I was only 6 when my great grandfather passed away. Back then (i'm 45 now), my family made me attend his wake/funeral. I had nightmares for years because he was so special to me, and I just couldn't bare the image of him in the casket. What they need is someone to explain to them that she's in a better place now, not in pain any longer and she's with God (if that's your belief). I hope this helps.. the best of luck to you and your sister. God Bless! Cheryl