Teaching who questions
Name the category before the answer: "Who means a person. Which of these is a person?" A child who answers a who question with a place or a thing has not yet mapped the word to its answer type, and that rule of thumb is the fix most often used.
Level 2 is where who gets harder: two people are in the picture, and the child has to use a detail ("Who is wearing the red hat?") to pick the right one. Level 3 moves to people who are not doing anything visible: "Who do you think made the cake?"
How the three levels work
Every question word has three levels, following the usual clinical progression from literal to inferential questions. Level 1 is literal and obvious, with two choices: point to a big thing in the picture. Level 2 is literal but needs looking: a smaller detail, a spatial word, telling two people apart, with three choices. Level 3 is inferential, with three choices: use clues in the picture plus what you know about the world.
Every question was checked against its picture: the right answer is plainly true in the image and every wrong answer plainly false. A session is 10 questions of one type and level, at most two from the same picture.