Single Series #1 (1938)
The above was acquired in a collection earlier this week, along with several other Captain and the Kids/Katzenjammer Kids comics. But that’s the oldest one in the bunch, the first issue of the series that would eventually become Comics on Parade.
You can read more about the Katzenjammer Kids comic strip at this comprehensive website.
And the strip is still running.
EDIT: Find more Captain and the Kids at Barnacle Press.