After dinner and my somewhat unsuccessful explanation of onomatopoeia, I turned to YouTube to try to find a video that might help my daughters better understand what onomatopoeia is. That's where I found this cute and short music video about onomatopoeia. I'll warn you, the song is kind of catchy (if you're a five-year-old).
On a related note, Next Vista for Learning hosts a great video explanation of onomatopoeia. The video was produced by a high school student for one of Next Vista's many student video creation contests.