understanding death

My son keeps asking me when Molly is coming home. Molly is our doggy that died on valentine’s day.
“She’s not coming home.” I tell him.
He then goes over to his toys and explains
“Molly is not coming home. Her heart was sick, and the doctor couldn’t fix her brain.” he tells them.
Which is true, except for the brain part. I’m not sure where he got that at. He then comes over to me.
“But Molly misses us.” he says.
“Yes,” I say “but she knows we love her very much.”
“Yes,” he’ll answer “and she loves us very much too.”
I nod my head.
He then goes about playing, sad that his puppy isn’t coming home, and not fully comprehending why. How do you explain death to a three year old. Especially such an unexpected death. Especially when you don’t fully grasp it yourself.
At one point during one of these conversations we had, as we have them at least a couple times a day, he told me
“Yes, but Molly will be better on the next day.”
“No,” I answer, “she died sweetheart.”
“But why?”
“Because sometimes things get old and die, and sometimes they get sick and die.”
“But why?”
“I don’t know sweetheart, I don’t know.”
I miss her too.. terribly.. silly dog.. but I think he breaks my heart more.. trying to understand things that he just shouldn’t have to. Stressing over her not being here. This continual constant in his life. This little ball of black fur that welcomed him home from the hospital, even though she was not quite sure what he was, and jumped back immediately when he began to fuss. His first best friend. In ten years he wont even remember her. He’ll remember things he’s been told, and he’ll remember her from pictures, but her herself he will not remember.. such is death, animal or human.. that when all those who do remember are too dead, then all is forgotten.. a cruel twist of fate.
“Mommy?”
“Yes?”
“But Molly wants to come home from the doctor now.”
“She can’t sweetheart.”
“But she misses us.”
(photo: Molly when she was a puppy)