After last talk with the organizor and the participation and interview in my tribe, I found that volunteer eager to hear something from the kid and the organizer hope they can have a way to measure their impact. Inspired by the Postcard Player which is a player can play the song on a postcard with conductive ink. Another relative work is Skai which is a playful media-interface designed specifically for the home that lets you interact with digital media using physical objects. You place objects in a wooden bowl to play back related media on the TV.
I got an idea about maybe postcard can contain more information like volunteer’s voice and their individual character. And when kid receive the postcard they can use a device to read the extra information and give a simple feedback through the device.