We have used name tags since we began workshops.
We thought it would be a good idea for the children to wear them so the monthly leaders could learn names. Since then we have added names tags for the teachers - so the children know who their teacher is.
We use those plastic stretch cord types and have a worm on them with the children's name in color - we don't have names for our groups - we just use colors.
The teacher puts the name tags on the table before the children arrive (this helps to separate some of the troublesome or chatty children). The teacher collects the name tags before dismissing the children.
Of course, because we rotate to a different room every week, I move the names tags and attendance sheets from room to room each week. We don't seem to have any problems- maybe because when we first met with the the teachers four years ago at our annual teacher training event in August we had the name tags ready and explained what to do with them.