What is the best way to organize a Kids Fundraising Event Scavenger Hunt?

We are planning on organizing a fundraiser which would be a scavenger hunt taking place at Fort York in Toronto. The idea is to have the kids and their families attend a fun filled event where they can all be involved and raise money for a non prfit charity. We would be expecting about 1000 kids under the age of 12 and their parents and families. We are hoping to build a list of ideas and resources that will help us brainstorm and plan this event.