A child may not consciously think about the art, aesthetics, or emotional impact of their toys (because they have not yet learned to do so), but a toy's design does have an aesthetic or emotional impact. Toys (and video games) spark the imaginations of children; when they play with a toy, they may project themselves onto it, or give it a personality and a name. They often visit fantastical worlds with their toys and build their own stories and adventures. A work of art is the same; a person can project themselves into a painting to explore its world, or attribute a personality to the subject of a sculpture.
Video games offer the same kind of experience. And unlike most children, adults who play video games can think very deeply about the aesthetic or emotional impact of their games just as they can any work of art. So if toys and video games can elicit aesthetic and emotional responses, they must also be considered art.