Supplies: Hard Boiled Eggs (enough for each child to have 1 or 2), dye-filled q-tips, trash-bags to lay out on the tables for messes.
I decided on the q-tips because the traditional egg dying dip sets was a bit overwhelming with the prospect of 12 girls and only 2 adults to supervise. The girls used the dye-filled q-tips to "paint" the eggs and this allowed a certain amount of freedom that egg dipping doesn't give. The girls were able to paint flowers, squiggles and other designs on their eggs.
A word of warning: Once the eggs ran out, the girls used the rest of the time painting their teeth with the (thankfully) non-toxic food dye. This activity would go better with either another craft project or a nice story about Easter.