Your kids say it because they are like me and realize how dumb they are relative. :)
As is said - old age and treachery will win out over youth and exuberance every time. ":^)
It's that sine wave effect of age vs perceived intelligence.
When you're really young, you think your parents are the smartest people on earth, and they think that you're the smartest kid on earth... then .... long about the time you reach 50 or so, the mutual admiration of each other's relative merits again co-incide...