For a school project we made a handeld console with a raspberry pi 2 and retropie. We designed an printed a case, which holds the pi, the 2.8" screen, the battery and a board for the buttons. We were inspired by adafruit's PiGRRL so it's not surprising, that we use much of the same components. We can really say they did a great job with that.
Our project should be really easy to reproduce for a young audience. For that we also created instructions to do so.
Because the instruction is larger than two 2MB here is the link to it: