One of their activities was to design a Magic card, and we think the cards they came up with are pretty interesting. Mark Rosewater took each group (8-10 years old and 11-17) and showed them twenty potential pieces of art. Once the art was picked by the group, they named the card. From there, they selected a creature type, a power and toughness, a mechanic, and flavor text. Finally, they came up with the card's mana cost, which is where Mark provided the most guidance.
The 8-10s picked Sickle Ripper's art right away and came up with the Reaper of the Dark Flame:
Meanwhile, the 11-17s picked Jace Beleren's art and renamed him "Kardoth the Impaler". Their theory was that he could turn his arms into knives and then throw the knives at people, resulting in this mechanic:
The smaller notes are the result of a quickie "Development" phase which cleaned up the wording on the cards before mocking them up. Each child that came to Wizards of the Coast got to take home a sheet of paper with shockingly realistic card images on it:
Not a bad souvenir for a day at your parent's job!