Here is a real life shoot out story for ya. A friend of mine works at a cop shop in a small town here in Texas. He told me the following.
Bad guy excapes from the Huntsville pen. Cops are out looking for him. A state trooper sees a suspicious car sitting in a road side park. He approaches, and when he reaches the drivers door. The guy inside starts firing a .38 special at him. Keep in mind that the cop is standing right next to the window. The cop pulls out his 9mm and returns fire. The bad guy empties his wheel gun. The cop empties his 9mm. Total damage. The bad guy got a bad scratch on his arm, as a result of some flying glass.
The moral of this story is. If you have the time, and money, to practice enough, to establish adequate muscle memory so that you are confident you will hit what you are aiming at. Even if you are ducking, and not aiming, per se, at all. Get a hand gun. Otherwise. I would suggest a 12 gauge Mossburg pump. Use 3 inch magnum loads, with #4 shot. Double ought clumps to much.
Oh, and BTW. Always. Always. Always. ID your target. AND your background. Getting shot will hurt a hell of a lot less then killing one of your children