I'll add...if you feel this way you should not get another dog soon. Any dog could and/or would do the exact same thing in a similar situation. You had 5 years previous knowledge of your dogs behavior and in one incident you kill him. Do your family and the next dog a favor and do not get another until you child is grown.

BTW, I'm all for protecting your family. I feel you did what you thought was best to do. But I would still not get another dog.