Here's an old story that the late Myron Cohen used to tell:
It seems this young (but not too bright) boy comes home from his first day at the Yeshivah (Hebrew School), and his father asks him what he learned. "We learned to say Kaddish, papa."
Well, the father is none too happy to hear this, so he runs down to the synagogue and confronts the Rabbi. "Rabbi," he says. "What is this about you teaching my son to say Kaddish? After all, he shouldn't know about this at so young an age, and besides, I'm a young man myself, in excellent health, and I expect to live a long time yet!"
The Rabbi answered, "First of all, it's not Kaddish, it's KIDDUSH! and secondly, you should only live so long 'till he learns it!"