Nope. Mary & Junior came years before Superboy and Girl. Junior was created in 1941 and Mary in 1942. Superboy first saw publication in 1945, and Supergirl in 1954.

And it's really weird that DC didn't go after Fawcett over Captain Marvel 'til Cap started out-selling Supes. DC started amping Supes' powers up because of Cap's popularity.:p