If you just wanted Hidden Mickeys in World Showcase, you can look for specific ones on their website: http://www.hiddenmickeyguy.com/catalog/epcot/world-showcase and you could put that in a scavenger hunt as well.
Sample...
Eat a dessert in Mexico
Find the cheapest piece of candy in Japan
Look for the Hidden Mickey in China that is located near...
Take a photo of yourself in a hat from Morrocco
Do Agent P in 2 countries
Meet a character in 1 country
Find out what language they speak in Norway and learn how to say "I have to go to the bathroom"
watch a live show in a country and then get one of the member's autograph
Sing the Star Spangled Banner outloud when you get to the American paviolion
You can probably find a few trivia questions they can answer in each country as well found on signs around the countries- I have seen these on the boards before but can't locate them currently
Sample...
Eat a dessert in Mexico
Find the cheapest piece of candy in Japan
Look for the Hidden Mickey in China that is located near...
Take a photo of yourself in a hat from Morrocco
Do Agent P in 2 countries
Meet a character in 1 country
Find out what language they speak in Norway and learn how to say "I have to go to the bathroom"
watch a live show in a country and then get one of the member's autograph
Sing the Star Spangled Banner outloud when you get to the American paviolion
You can probably find a few trivia questions they can answer in each country as well found on signs around the countries- I have seen these on the boards before but can't locate them currently