A coloring book teaches a billion times what a coloring app can teach. How materials feel, how to use haptic feedback to not break a crayon, how objects create sound as they touch, how different materials interact (eg pencil vs crayon), how friction changes based on force normal to the surface, how materials hardness affects abrasion and changes the shape of the crayon, how different items have different colors and how these can transfer between materials, etc...

Kids 2 to 4 should not be using screens. They have too much to learn.