Tintin in America was a little dark. We've slowly been accumulating the books for our three year old, and we got about half-way through that one when we decided to put it away til he was older. The concept of a lynching is just a little beyond a toddler :-P
The rest have been wonderful for him though. Also, if you happen to have a tv that displays PAL/SECAM it's well worth it to seek out the DVDs of the cartoon series. They include the english language tracks and are very faithful to Herge's books.
If you don't mind watching them on your computer, you can reset the region of your DVD-ROM reader to region 2 and just buy your DVDs from Amazon.com in the UK.
If you get into watching films on PAL DVDs, you'll find that you get more resolution and non-interlaced frames...
Plus, oddly enough, I have found that the movies that I like are actually cheaper in the UK, even when you include shipping.