"Small Planes" joke

A mother and her son were flying Southwest Airlines from Kansas
to Chicago. The son, who had been looking out the window, turned
to his mother and said, "If big dogs have baby dogs and big cats
have baby cats, why don't big planes have baby planes?" The
mother, who couldn't think of an answer, told her son to ask the
stewardess.
So the boy asked the stewardess, "If big dogs have baby dogs and
big cats have baby cats, why don't big planes have baby planes?"
The stewardess asked, "Did your mother tell you to ask me?" The
boy said that she did. She then said, "Tell your mother that
Southwest always pulls out on time."