The Writing Site has a good list of poetry-writing prompts for children at different grade levels. If you're teaching this April and want to include a section on poetry, this article might be useful. I'm all for kids getting into poetry early. I did, with Dylan Thomas, the Japanese haiku poets, and even Wallace Stevens (couldn't make head or tail out of the poems but I loved the sounds the words made and some of the stranger words).
Speaking of early impressions, this E.E. Cummings poem
made its mark on me when I was an early teen. The fresh use of words and syntax opened my eyes to new possibilities.
The photo exercise is another prompt. Select a photo and write a poem from it. I wrote one, am going to try another this week.