This study on rats suggests that exposing children to diet foods esp those with artificial sweetners may disrupt satiety mechanisms and even contribute to obesity in later life.
I find it convincing because there are a host of adult studies showing that the body isn't as easily fooled as Aspartame manufacturers would have you believe, and in fact, eating and drinking artificially sweetened products do not trick the body into feeling full or satisfied, so you take in just as many calories overall as someone who eats/drinks sugar-sweetened products.
I really dislike artificial sweeteners and rarely let my children have them - this has strengthened my resolve!
www.ctv.ca/servlet/ArticleNews/story/CTVNews/20070808/lowcal_obesity_070808/20070808?hub=Health