We talked about life cycles (butterflies, frogs, humans), but what my kids enjoyed the most were the hands-on examples. Releasing a butterfly and chasing it until you run out of yard.
Then, we talked about shrimp migration and how dams pose a problem to this process. The kids were given yardsticks, marbles and two tents- one for downstream, one for pipe. The marbles represented the shrimp. If a "shrimp" went through the pipe, it was dead and out of use. The ones that went through the downstream tent, were rolled again. The kids kept rolling until all the shrimp went through the pipe. They recorded how many "died" on each turn.
I was with the younger set this time around. We had fun rolling our marbles without worrying which "tent" they went through. Their only concern was someone else picking up "their" marble. They all looked basically the same to me, but magically the kids knew exactly which one they had rolled.
Michael was pretty good this time...he really enjoyed this puzzle.