Of course, all that relies on you not seeing the "dot, dot, dot"
part at the beginning of the quote, which is why I spelled it out. The intentional use of ellipsis on this part is a trick that the NRA has been using for decades that more and more people have finally caught on to. That first part says that gun ownership is permitted in the context of a "A well-regulated militia, being necessary to the security of a free state". So, for those who think that the primary purpose of having a gun is protecting themselves against the government, no, this right, granted by the government, is intended to be regulated by the government. If you plan to use your gun to overthrow the government then that is not covered by the 2nd Amendment. Also contrary to conventional gun-nut rhetoric, you will note that the purpose of the 2nd Amendment is not to provide for individual protection, but rather, it is explicitly to provide for protection of the state against those who would undermine it.
As to the issue of 5-year-olds with machine guns, the state can regulate that precisely because no well-regulated militia would want or need infants carrying firearms. Likewise, none of them want the mentally ill to be toting around massive fire power. Congress has the power and the responsibility to regulate fire arms, and lets hope that they finally do their job adequately, and intelligently this time.