With children possessing a natural uncanny ability when it comes to horror, perhaps we can push this further by making the humanoid baby a doll/puppet. Dolls and puppets are perhaps even more uncanny in their strange likeness to humans, and whether they are 'alive' or not.

Chucky from Child's Play springs to mind as an initial point of inspiration, capturing the creepiness of dolls with a true sense of horror.



The puppet from Saw also features uncanny characteristics in its stillness and ever so subtle movements.



The arms of the baby doll could be tweaked to be a chainsaw blade itself, perhaps the result of some mad experimentation to bring the puppet alive similar to that of Shelley's Frankenstein. Check out the 1910 version of Frankenstein below.



The doll/puppet idea could be worked to be a parody to the cliche of murderous dolls as a full scale horror, or perhaps even comedic depending its style and presentation. Whether its plausible to go down this route is up to discussion.