If you give the audience a roadmap right up front, and tell them how you want them to interact with you, you will maintain control of the presentation.
If you have a highly interactive session, you need to share up front with the group how you will bring them back together as a large group. This will save anyone the embarrassment of having to be called out in front of the group and it will save you from looking like a whiny child demanding attention.
So you might tell the group, “Throughout this time we’ll be doing many activities. In order to ensure we stick to our time schedule, whenever you see my hand up in the air please quiet down and put your hand in the air. Once we have all the hands in the air we will pull back together as a group and move forward.”
Remember, most groups want things to flow as smoothly as possible. This means that as a leader you need to be very clear with your directions for any group activities.