No matter what kind of shot you use in the shotgun, it will not open up enough in a home defense situation to make up for poor aim. Unless you have an illegal length barrrel. Freddy is right about what the experts say but I think anyone hit with a load of number 4 shot will be not so dangerous afterwards. And the smaller shot will not penetrate walls with as much lethality. Hit them in the face and you blind them permenantly. Be sure and kill them because they will sue you for ruining their lives if you maim them. Lots of lawyers looking for those kind of cases. We can talk about what/where/when all day but the best thing for anyone arming themselves is to get some instruction and practice.
I would like to address the concern of children and firearms. In this rural area in the 60's, every home had guns. All children were raised with the guns standing in the corner or multiple corners. No one had fancy locking gun cases. I would like to be able to tell you why we did not "play" with the guns and neither did my friends. It is about the quality of the parents I guess. No one touched the guns!!! We had bb guns at about 10 years old and they were our training. When you make guns so tabboo or unusual or mystical, they are an irrresistable thing for children. Just the same as many kids go out and drink like fish, do drugs, have unprotected sex, etc, etc.
One of my friends at college was from Spain. He was accustomed to drinking wine and beer with dinner and meals. He was only 18 so he was illegal here in the US. His parents came for a visit and bought him a bunch of stuff to stockpile under his bed. He had a totally different attitude about alcohol then the American kids. It was not forbidden. It was not mystical. It was best had in moderation. One of the things I have learned from the many international students I have met over the years is that they are amazed how immature the kids are here even if they are the same age. We try to keep our kids "kids" to long so they have to rely on us longer. It shows in the work ethic and raging drug use and lack of maturity of the present American youth. We have relied on immigrant's childeren for our best and brightest for some years now. They are motivated.
So, do what you like with your children, but keeping them innocent and ignorant will not pay off in the long run because they will grow up and have to face life whether you like it or not.
Just my other 2 cents worth,