from Action Comics #40 (September 1941):
And then, in the following month, there was the first issue of Star Spangled Comics:
For those of you not all that familiar with the original (Golden Age) version of The Star Spangled Kid & Stripesy, they were just a couple of non-powered costumed crime fighters. Premiering in 1941, still a few months before the U.S. had formally declared war on Japan and Nazi Germany and officially entered WWII, they wore the colors red, white, and blue and used other aspects of the American flag for their names and their costumes. But unlike many duos where the adult was the main lead and the kid was the inexperienced sidekick, Star-Spangled Kid and Stripesy reversed that dynamic by making the younger member the main decision-maker and the adult was basically his "sidekick".
As for those of you wondering what happened to Sylvester having a cosmic rod / cosmic belt to give him more power (and something that would eventually get passed on to Courtney Whitmore), Sylvester wouldn't gain that ability until the mid-1970s.