Up until having my own child, most of my experience in working with children came as a baseball coach. I was first hired by the city of Corvallis (OR) Parks and Recreation Department to lead a team of 4-year-olds when I was only 14 myself. I subsequently went on to coach some 40 more teams during the next 15 years.
Parents at Woodland Park notice that I do a lot of, "C'mon everybody. Let's go over here!" types of things, which is a carry-over from coaching where the focus is on team building. In preschool, I suppose it's better called "community building". In our 3-5's class, this technique stimulates large group play, but in the Pre-3 class it functions in a slightly different manner. That's because most 2-year-olds simply aren't developmentally geared for cooperative play, so following Teacher Tom around the classroom becomes for some kids a transitional stage between parallel and interactive play.
As we run around the playground playing firefighter and putting out "fires", for instance, the dynamic may look like kids playing together, but its really just many individual kids playing with Teacher Tom at the same time. That said, we are playing together at least on a superficial level, something upon which we can build as the year rolls on.
During the first few months of the school year, my "skirt" of children grows as more and more children decide to hop on the Teacher Tom bandwagon. Ultimately, however, the goal is to start shedding members of my entourage as they're ready. By the end of the year my expectation is that the children will be so engaged in their own activities that I'll be able to just lean against a wall and watch.