I think in terms of layers of defense. Let's assume that multiple bad guys have already put together a plan to kidnap your children. For some reasons, they have decided to take them from the house in the middle of the night.
Bedrooms on the second floor. Install automatic exterior perimeter lights, a sprinkler system that can be activated from your "safe" room, a fence and a large dog. A four camera video system with the display in your "safe" room will give you eyes. A cell phone in your "safe" room for reliable communications. Keep your shotgun in your "safe" room, which has a door with a deadbolt. You need something solid to hide (from bullets) behind at the top of the stairs, your first place to put-up a fight and in your safe room. You may not be able to retreat to the second floor; therefore a secondary "safe" area must be located on the first floor. You need to practice what you will do when in harms way. Training and regular practice for both yourself and your wife. This means home practice and range practice. Also, general awareness of your surroundings might alert you to potential problems. You must have an exit strategy. What happens if they know that you will retreat to your "safe" room and they have decided to just smoke you out, or throw tear gas through your bedroom window? How about a fire supression system and carbon monoxide detectors? Many more families face fire than face armed entry. To construct a bulletproof room is not really a critical component.
Last question: What do you do when you and your family is in the yard, or away from home?