"You have to wonder if the designers of the "speed bump of the future" considered that drivers might become conditioned to disregard Pavement Patty and her imaginary cohorts, creating something similar to a "boy who cried wolf" effect. Couldn't such conditioning reduce drivers' caution if a real child should cross their path?"

That's all there is to this. Drivers get used to the illusion, a real child gets hit soon enough.

This will likely habituate drivers to images of children playing in the streets.

Or to running over images of children playing in the streets. Also, tourists are going to be really scared when a cab driver just ignores one of those.