Charlie's son appeared in the earliest strips but Alfred Andriola replaced him with Kirk Barrow. Apparently he wanted a Pat Ryan-style he-man to handle romance and physical violence, neither of which were up Charlie's alley. Andriola felt constrained by Chan's passive personality. I don't have the exact quote, but he once wrote something to the effect that Oriental philosophy is a lot less interesting than a .45 automatic.
Link to the book:
Charlie Chan Daily Newspaper Strips 1939-05-22 To 1939-12-23