It sound like you are talking about a sort of cereal dessert buffet including really colorful, "bad for you" kids' dry cereals. Here are some articles with great pictures of various set ups:

boards.weddingbee.com/topic/cereal-buffet/#axzz37IroWAVs
www.seriouseats.com/2012/08/gramercy-terrace-cereal-bar-nyc-breakfast-gramercy-hotel.html

www.cereality.com/main.php
See especially the menu page for inspiration!
Their Facebook page is:
www.facebook.com/Cereality

You could go with a dozen or up to 30 varieties of everyone’s favorite quick-and-easy breakfast choices—from Cocoa Puffs to Special K to Cap’n Crunch, inviting people to mix and match.

Toppings? sliced strawberries, blueberries M&Ms, yogurt, sliced bananas (dip in orange juice to prevent browning) and many more- look at my ice cream sundae bar page for more ideas

Icy cold milk, maybe put the milk in the freezer for a few minutes before putting it into big bowls of ice-using wine carafes, maybe- skim for the healthy, chocolate for sugar fiends, strawberry milk, Peanut Butter Milk, and vanilla soy or almond for the non-dairy people. Glasses- could be shot glass size- for drinking some, if desired.

A make your own granola station is an additional option, raisins, coconut, dried fruits, etc.

Yogurt and ice cream for cereal parfaits?

You could present the cereal in large old-fashioned glass jars with lift-off lids. You can get these at Target - they look very rustic and are great to serve ice tea and lemonade in as well. Hold about 2 gallons of fluid. They're thick glass and heavy which helped to keep them from falling over from the kids scooping out the cereal. Small metal "scoopers" placed in front of each jar and different levels of colorful cereal selections. The glass lets you see what you want as you approach the bar. The bowls are presented with the spoons at this bar.

An alternative is to serve the cereals in (plastic-lined) galvanized pails or large plastic beach buckets. If you are going with the bucket idea, you could use small shovels/scoops as for beach sand. You could add metal troughs, and decorate with mini hay bales, checkered cloths; or go for a beach theme? Maybe find some of those old fashioned glass milk bottles for the milk.

This is breakfast for 100 people:
Cold cereals
these are teens, so I would say, 1 pound per 6
3 1/2 gallons milk or soy milk for the the cereal

Many will take a full 8 ounces of juice unless you only have 4 ounce glasses- 1 quart per 4- nearly 2/3 oj, 1/3 apple- but with all the new juices, take a look at the many other choices; and if you offer crushed ice people will use it

for drinking milk, 4 gallons per 100

Yes both muffins and donuts would be fine, possibly mini muffins- see the breakfast planning page for help.