Mamas, I found a sweet and lovely website that's truly for children of all ages. (Via How About Orange?) It's call Bzzzpeek and it's a "collection of onomatopoeia from around the world." They present sounds of animals and vehicles, recorded by children, from all over the globe, and present them side by side, which serves to highligh both similarities and--sometimes hilarious--differences. It's a really cute exercise, and there is even a place for you and your kids to submit your own sounds.
And they sell these super cute t-shirts!