As a sophomore team that doubled in size, we are in the same position. It’s hard to keep the attention of 10+ people at one time. We try to break out into groups of 4-6 so everyone gets to be hands on. Sometimes we pair up a senior member with a rookie member.
Pick a topic that you can demonstrate in about 45 minutes. Last night, we went through the 2016 pneumatic manual in the FIRST resources online. We worked on a piece of plywood and ‘built’ the system from there. It didn’t do anything but extend a piston, but the members were able to see all the parts being used and assemble them for themselves.
Another night, we took 45 minutes and went through the powerpoint in the FIRST resources on manipulators used in FIRST.
http://thinktank.wpi.edu/article/28
Lots of great photos and really easy to give, especially if you have experience in FRC, have a bot that used one of these strategies, have the materials around to mock up some of the ideas in the presentation.