They are now. They don't have to be.
My kids are bright, but not geniuses. This is what we should be expecting. Start early and they can do it. In 19th Century America, it was not unusual for children to read well by the age of three.
I submit that the composition of the population that the U.S. has now, compared to what it was in the 18th and early--and I accent "early"--19th century is so different that what you are doing absolutely cannot be done except by a few of the upper middle class. The lower-middle class, lower class, and the very poor don't offer much in the way of raw material, knowledge, and interest in doing what you did. It does have to be as it is.
I believe that the authors of "The Bell Curve" had it right: intelligence is largely a function of heredity. Otherwise, you could stop someone at random off the street corner and make him or her a nuclear physicist.
I do heartily congratulate you for what and your spouse have done but--and this strikes me as extremely sad--only a tiny, tiny percentage of the American population can do what you did.