In the past, I have run several workshops at elementary and secondary schools. The aim was exactly, as you so nicely put it, to show the kids how much fun we are having (although the first time I did that, I hadn't even started university yet). So let me tell you a personal story.
My experience, which comes from dealing with three different schools in two different countries, is that you don't need any connections at all! In all three instances, I just contacted the head masters of the schools and told them "how about I do weekly maths/logic afternoon workshops for your kids" and they always gratefully and immediately accepted. It was always my choice for what age group, how long, how often, and about what specifically the workshops were supposed to be. So go right ahead, pop into the next school you pass on your way and ask to talk to the headmaster.
As for reaching grown ups, the first workshops I conducted were for 9-10 year olds, I myself was mere 19 years old. I always gave the kids "homework" and they always came back the next week, telling me how their entire family, including older siblings and parents, enjoyed solving the puzzles. At the end of the workshop (that is, when I decided to end it), the headmaster told me that she had received several requests from the parents, whether it would be possible to initiate a similar workshop for them. She indicated that the school was willing to provide a room and the material that I would need. Unfortunately, I was about to start my civil service, so this never came about, but it obviously would have done if had so chosen.
One more thing: the kids didn't let me go after the last session. They literally clung to my legs and kept asking whether I would do the same thing the following year (which I couldn't because I was about to begin my undergraduate studies abroad). The moral is that these workshops have been one of my most gratifying mathematical experiences, so I recommend this to anybody who considers it, even out of completely selfish considerations. Please help yourself liberally to the material that I used and that you can find on my website. Please also let me know by email if you do go ahead with this. I will be very grateful if you could share your material and ideas with me.
