Sometimes I think that I became a teacher for the adrenaline rush. For your students, this can be a terrifying experience. Let them use these as opportunities for exploring their fear. Low risk situations like this can be wonderful confidence boosters. Naturally, you must ensure that they are low risk.
Closure is often the toughest part of a presentation.
Use the opportunity to review the most important points, generate some higher level thoughts, and stimulate some critical thinking skills. Ask questions of your audience. Make it seem like the time they spent listening to you was valid. Most of these tips will probably be second-nature to you as a teacher. But your students will hopefully be creating and giving their own presentations.