Two-Year Man
ShortStory 4,773 words Recommended by 3 award/anthology sources
Mikkel isn't very bright, but he cleverly supplements his janitorial job by scavenging useful items his superiors discard and bringing them home to his wife--then one day he brings home a mutant baby.
Quasar links out; the story lives on Asimov's, where the author gets the click.