Kids Warmer: Stand up, Sit down
Tell your students that you'll be asking them some questions and rather than answering 'Yes' or 'No', they should either sit down or stand up.
Start off by asking some very easy questions:
Do you like cats?
Can you fly?
Do you go to school?
Are you 50 years old?
Once they have gotten the idea, ask one of your stronger students to go first and sit in the teacher's chair. They now start asking questions to the other students.
Each student gets three questions each before you bring someone new in. It's not necessary to have every one of your students ask questions, especially if you have a large class. Just keep going until the class is warmed up and then move on.