Before you can get anything done, your team has to get to know each other. They are individuals bringing different talents and interests into the mix. They also have to feel like a team, working together to solve a challenge. The best way to accomplish this is to schedule a number of activities that allow them to have fun together.
Games like “Apples to Apples” (available at most stores) and Charades are good for older elementary level and up. For Charades you prepare strips of paper ahead of time with the names of currently popular books, movies, TV shows, famous people, etc., based on the interests of the age group you are working with. The team members take turns pulling a slip of paper and then silently acting out the title or name on the paper. (see http://en.wikipedia.org/wiki/Charades for complete description and rules)
Younger children can be instructed to act out various animals for the other children to guess. Encourage them to move around the room, using their whole body. Some kids really get into this. Others are shy. That’s OK. The idea is to have fun and start to feel comfortable together. If they seem reticent or confused, start things off by demonstrating yourself. After they see their team manager crawling around on the floor, they should loosen up.