A friend of mine asked me today, "what should I tell the kids?" and this was about their dog, the family pet, a member of the family. They were taking their dog to the vet and wondering if they should tell the kids... that they were going to have to put him to sleep.
I understand that not everyone will agree with this, so please remember this is just my perspective...
I believe we should never underestimate children. I would leave it up to you to determine how much information you think they can truly handle, because you know them best. Some kids, regardless of age, can accept the truth and are oftentimes better for knowing it.
I spoke to a woman about a year ago, her father was dying and she too asked me the question of what she should say to the kids and if they should come say goodbye. She told me a story about how her grandfather died when she was little and no one told her until days after, and she never got to say, "goodbye" or "I love you" and she has never forgotten that. I told her she knew the answer... and she did, and the kids sat around his bed and said goodbye (they were between 3-16).
Here is my advice. Tell the truth, always tell the truth. And give the kids the opportunity to say, "goodbye" and "I love you" when they still can. They might say no, but at least you gave them the choice. When we don't communicate or explain, or ask, we take their choice from them, and this could be something that they struggle with for the rest of their lives.
As I am writing this to each of you, my friend called to say that she decided to tell the kids before they took their dog in. The kids were sad, but asked if they could say goodbye. They both curled up around the dog on the floor and told him how much they loved him, they thanked him for being their friend, and they told him they would miss him. (they are 5, and 7)
Not all children can handle this news, so it definitely needs to be carefully considered, but my advice would be to never assume, and to at the very least, give them a choice as to whether or not they want to say goodbye. Never assume a child is too young or too old to grieve.
Whether it is family, a close friend or a pet (who is also family) that kind of loss is deep, and it stays in your heart forever and if given the opportunity to at the very least say, "goodbye" I think everyone deserves that.