Other things I've done to go along with the Sermon on the Mount:

• We talked about how Jesus' teachings turned the teachings of the day "upsidedown" ("You have heard that it was said... but I say...). We discussed the way our society says things should be done. I said "upside down" A LOT! We have a gymnast among our kids, so every time I said it, she did a back walkover. She loved being a part of it, and the kids were saying "upside down" so she'd do another one. 
• We talked about how Jesus' teaching was surprising. Blessed are the meek?! Be kind to mean people?! We did several easy, quick and SURPRISING experiments (I have preschool through 3rd grade all together in one class): made pepper run away, made a needle float, etc. Then I let the kids come up and put a drop of food coloring in a glass of water and tell about a time they might have been tempted to do wrong - get revenge, hit my brother, etc. The water looked dark greenish blue. Then we talked about what the Sermon said to do instead. For each good idea, I poured in bleach. We talked about how it makes us feel to do the right thing, how hard it is, and what things help us (God's word, his promises, friends, etc.). As we talked, the water faded back to clear. (It took a while. Which was part of the point. Sometimes in the moment we don't feel so great about it.)