Take a grass flower stem and pinch below the seeds with finger and thumb. Run the finger & thumb up the stem, removing the seeds. Present the seeds (which should now be bunched between finger and thumb) and then flick your thumb causing the seeds to fly up in a shower... Suit the actions to go with this rhyme:

Here's a tree in summer,
Here's a tree in winter (strip)
Here's a bunch of flowers (present)
Here's the April showers! (flick - preferably over the audience)

We used to make poppy ladies too... I was always disappointed at how quickly they lost their lustre and wilted.

LTS