Happy Mutant 3-Armed Baby Costume

Step 3 Find suitably-sized doll

A similarly-sized doll can be useful in sizing the costume for your 3-armed baby.  We'll use one of its arms to mock up the outfit, though of course we'll substitute Corvidae's real third arm when she wears the outfit.

This doll has realistic plastic hands, and a cloth body - perfect for our purposes.  Choose the hand with the most realistic positioning.