Use the who flash card when you begin to explore compound phrases with your child. This sign is best for toddlers, and we use it when teaching relational ideas. For example, you can ask a toddler, "Who did it?" or, "Who has it?" when referring to an object.
Teach your toddler the who sign when they can already grasp more complex relational ideas. "Who got your crayons?" "Who is that in the picture?"