Sadly, a deterrent is unlikely work, you could make it a capital crime and it would still happen. It may reduce some peripheral activity but the person who carries out acts against children is, by their very nature, thinking outside the parameters of most people in society. They do need removing from society at the very least, children are the most precious things in the world and should be protected above all else.
I can only imaging the despair and fury that the parents must be feeling, I would find it very difficult to behave in a restrained manner if I were in their position.
They have just announced on the radio that the man in custody is being now being held for questioning re murder.
EDIT; What Mikey74 said^^^