The Fish Died and the Kids Don’t Know. Now What?

So this happened.  I made the discovery that our pet betta fish was deceased, lying on the bottom of the fish tank, and the kids weren't home to see it.  They liked Maddox, and they would go into that room every day to feed him and check on him.  Dang it!

Aren't dead fish supposed to float?  Our beloved fish Maddox sunk right to the bottom, but there was no mistaking he was gone.  It shocked me.  I went in there to feed him because the kids didn't that morning, and there he was motionless on the rocks.

Anyway, I'm faced with the dilemma whether to tell the kids, or just go to the pet store and get a new fish.  After talking it out, I think I know what to do.  Would you do the same thing?