You miss the point. The 7 y/o isn't the issue. I'm trying to convey that there is no magic number of rounds that would be enough for every scenario.
I have seen police shooting videos and read reports where a trained officer misses multiple times on a single suspect. In one, the suspect wasn't even shoot at the officer but had a deer rifle point in his direction. Here we have someone trained, armed and in the mindset for a possible encounter. They are in the best possible position.
Additionally I have also seen video and heard reports of shootings involving multiple officers. They sometimes have given the number of rounds fired by the officers and it will be dozens. Obviously they missed a large percentage of the time.
Now, you take regular man or woman at home when 3 or even 2 intruders break in. They now have 10 rounds to deal with the situation. They probably have no training, will not be as well armed as the officer and do not have the mindset. They will be stressed and may be under fire. Yet they are now in a position where they must shoot just about perfectly to stay alive. They are in the worst possible position.