You can tell your son about death, and that it happens to every living thing at some time. Plants die, people die, and pets die. But we love them, and the love they have taught us lives on in everyone whom they loved.

I do not know if you or your Dad have any religious beliefs, but if you are Christian, you can explain heaven and God a little. You don't need to go into a lot of details or have a giant theological discussion, just explain that that is where good people go when they die, and he'll be reunited with the ones he loved.

Most of all explain that you love your Dad, and may be sad and need a few extra hugs. That gives him something concrete that he, as a little boy, can do.