My mother died five weeks before my daughter was born and my father died when she was 3yo. My daughter was very involved with the situation, since my Dad had ALS and died within months of the illness showing symptoms. He was a young 68yo. My sister and I took turns taking care of him 24/7 for a couple of months, bringing our daughters with us. My daughter gets sad and misses Grampy, sometimes at unexpected moments, because she remembers how fun he was, and how she enjoyed going to his house in NH. She's now 6yo. We talk about Grampy and remember the good times, because we don't want her to forget him. Even though he loved her, he died, and that's just part of life. It's important to acknowledge those moments and allow your child to express what he feels, even if it's uncomfortable for you to talk about. At his age, he probably now realizes that he isn't going to see his grandfather again in this life, so he now understands what death means, where he probably didn't grasp that when he was 3. He probably sees other kids with their grandparents and how much fun they have doing things together, and that may make him sad too. He may also be worried that something is going to happen to you or your husband, which is why he probably didn't want you to leave him at preschool. You need to reassure him that you love him, that he will be taken care of. You can't actually guarantee that nothing will happen to you, but you can soothe his fears now that he's figured out what death means. It helps to talk about your beliefs and not avoid difficult conversations about death. Best wishes.