Siegel and Shuster had little to do with the debut of Superboy, although they are credited in More Fun 101.
Siegel was in the Army at the time. Shuster was aware of the story.
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1945 Comic book More Fun 101 introduced Superboy - Superman when he was young. Superboy was not part of Siegel Shuster contract. Siegel suggested it but DC said no. DC used character while Siegel was in Army.
1947 Court Case As 10 year contract nears end, Siegel Shuster sue DC for rights to Superman and Superboy. They lose the case and are fired by DC.
From my
Super Hero Genre History