The basic device is a paper cutout that fits over the span of one octave starting at any C key. This is important because the C major scale is generally the first scale encountered when learning the piano as it does not include any black keys. It provides key labels for the user, but it allows acts as a base for a number of possible "shields." The basic device and a shield are shown above.
The chord shield helps the user find simple triad chords within the major C scale. Though the visual language needs improvement, the basic idea is to show finger positions of the I, IV, and V chords so that the user can quickly play a more substantial-sounding piece of music. I developed an additional shield for learning "Mary Had a Little Lamb" but, again, the visual language is at this point non-standard and could be more confusing than helpful.
Overall, I think there is potential in such a template that anyone could print or measure and draw themselves. It would be a good exercise for kids to use math in the creation of the paper cutout, and then give them a reward by enabling them to play notes and chords on a piano without needing any formal instruction.