One classroom I visited had made the shape of a big whale or fish on the floor using tape. The teacher then instructed the children to sit in that space. Another option is to do what my wife and I often do on retreats - we bring an attractive (but cheap) woven plastic oriental mat that we bought at a Korean grocery store. This is especially good for missions time. We have Bible time sitting in seats and then, for a change of pace, we all move to the foreign-looking mat for missions.
Generally, these methods work in keeping the children from moving around too much. Of course nothing works better than coming to club or class well prepared and delivering an exciting lesson.