I found a pattern for the invitations online and tweaked it a little. I printed them on cardstock and laminated them to look like credit cards. Here's a sample of the front and back (click to enlarge). ("Jane Doe" would have been the invited girls' name.)
I also made t-shirts for all the girls. I printed the image on iron-on transfer paper designed for dark shirts (so that the white part would show up). I printed the words on iron-on transfer paper designed for light shirts. I thought they turned out really cute and it made it easy to spot the girls as they ran around the mall.
Because I didn't want the girls running around the mall alone, I solicited the help of Alyssa and some of her friends to serve as Team Captains (2 of the other helpers had siblings attending the party). This worked out really well. I think the older girls had just as much fun as the younger ones and it freed me up to get food ready while they were doing the activities. Here's a picture of all the girls in their shirts and the helpers.
I divided them into teams of 2 and handed them their first set of 6 clues. I gave the teams the same clues but in different order so that they wouldn't all be doing the same thing at the same time. Here's what they had to do and some random pictures of each activity:
In addition to the first set of clues, I had 4 bonus clues that they could do for extra points.
While the girls were doing the first set of clues, I ordered lunch from Chick-Fil-A and had it ready for them. They ate lunch and visited a little bit and then we went on to the second set of clues. I re-selected the teams for this round so that they would get to be with someone different.
I got the most flack about the bubble gum challenge, but that one (by FAR!) had the funniest pictures, so I'm still glad I included it. :)
After the second set of clues, the girls ate a cookie cake (purchased from the Great American Cookie Company in the mall) and I gave out prizes before the parents picked them up.
The party lasted 2 hours, which was a just enough time to get all the games done and still have a little bit of time to visit. Best of all, we weren't out in the heat!