Henry Kuttner & C L Moore's "Baby Face" (novelette, body snatching, free): "Baby's Day Out", from many decades earlier
Story summary.To figure out why a baby is crying, a mad scientist uses his latest invention: to exchange the mind of his friend, minding the baby, with the baby - so friend in baby's mind can find out what is wrong!
That's when Nazi spies steal the brain exchange gadget. So we are left with: the grown up man is in baby's body, baby in grown up man's body, & scientist injured & unconscious. And the man in baby's body overheard the spies will pass on the gadget to a contact on circus that night.
So now it's up to the hero, in baby's body, to ensure the gadget doesn't fall in enemy hands...
Fact sheet.First published: Thrilling Wonder Stories, March 1945.
Read online at UNZ.
Related: Stories of Henry Kuttner, C L Moore.