I'm starting this discussion on the teaching and learning of Chinese, primarily because I teach the language to primary school students in Singapore. However, some of my pupils face some challenges in learning the language since they speak only English at home.
I worked in China for five summers and found the four tones hard to master, and when I took Chinese classes, my tongue couldn't hit those S sounds to save my life (Xie Xie). However, I had an easier time with the characters. All this to say that I have taught some nuggets of Chinese to second graders and they LOVED it. The teachers said they were smitten by it, thus it seems like the perfect time to teach tones and not have to unlearn like I did. I've got some pictures from China on my blog at http://ppsblogs.net/brianmckee as well as my Classroom 2.0 page. Good luck!
If you have iTunes, check into The Virtual Staffroom podcast. There was an episode "I Like Chinese" that was really good. It's not at The Virtual Staffroom website yet, but I'm sure it will be soon.