I detail the entire process below. I suggest that you start out with a photo of your child that has some depth of emotion. This will make your end result more interesting. In the photo of my daughter, I caught her while she was listening to a tiny rock. It was egg-shaped, so I suggested that there might be an egg inside. She then promptly put the rock to her ear and I snapped a photo of her in a deep state of focus.
Here's the first image I took: