Children are curious about how dead things operate, because they need to know what dead really is like. Handling a dead animal is like investigating the insides of a wide up toy. It is a child's way to sort out the real from the imagined. It is hard to speak to children of rotting and of bones. There is no way though to get around it.
Dead bodies get smelly and rot until only bones are left.
This happens to dead animals and to dead people. It is important that children are informed immediately. They should be told by parents or someone very close to them. Sad news needs to be relayed in familiar surroundings, preferably at home. Delay only makes it more possible that the child will be told of the death by the wrong person, at the wrong time, and in the wrong way.