How about " It's a small world, after all?" .. promotes ethnic diversity, the world as one, and so on... You could have the music playing, and kids could ride in a simple trailer, and all be dressed in different ethnic costumes. They could make flags out of poster board and attach to the sides of the trailer

We are going to participate in the city's annual halloween parade this year. This is the first time in 5 years that we are offering this voluntary activity. I need ideas for a small float and theme. Because we have many different economic backgrounds in our school, we are trying to keep it simple and make it something where the "costumes" can be made by students/pto. Not sure what the participation level will be, but I want to be prepared just in case. No scary, ghoulish stuff -- just something fun but not too dorky (my daughter's words exactly)LOL.