It's hard to put that up against a generation who has a lot of instant gratification when it comes to their experience with anything technology related.
And I had to walk uphill both ways to school... Some of you are proposing you spend 20 minutes with the kids speaking down to them from an ivory tower, using such words as "scary", "don't", "can't". If your aim is to turn off kids to computer science that is a good approach. Yes it is true, you must work hard and display patience. This should not be news to them and if they don't embrace this at some point they will not be successful at anything. So lets not pretend we are special.
You can tell them that computer science is not an elusive club. That their story does not have to include TRS-80's and main-frames and being geekier than the next. Given the time allowed and audience I'd speak on higher levels. Such as computer science is really fascinating because it is constantly evolving, as such you are constantly personally evolving. New challenges keep things fresh and create a wonderful sense of satisfaction. Tell them about what makes you successful in computer science, and be passionate and positive. I trust that if you do this both you and the students will wish you had 20 more :)