Many of our math circle students are mentoring or coaching younger students. Here are some excellent model examples of presentations to inspire you.
Ina Petkova (Columbia math PhD student) gave a very elegant, simple and clear exposition of a proof of the Pythagorean theorem that middle school students should readily be able to understand and later to recreate for themselves. The Girls' Angle program in Cambridge Massachusetts created the video of her presentation as the first video in their series. I look forward to seeing more on their website in the future.
Richard Rusczyk has many excellent video presentations which you can watch on the Alcumus section of the Art of Problem Solving website, but you will need to solve some problems first in order to earn the right to see them. What I like about Richard's presentations is that he doesn't just demonstrate the "nice" way to do a particular problem, he also shows some of the not-so-nice ways we might initially think about trying. It's important to acknowledge to students that we don't always know at the outset exactly what approach is going to work best for a given problem. There's a certain amount of groping about that is often necessary to get insights into a good method to solve a problem. We need to demonstrate that problem solving is a process, not just a magic bag of tricks.