Well there is already fluoride in our water, which is a poison. However drinking pretty much anything diet (even flavored waters) brings in the poison aspartame (ie. Splenda and other artificial sweeteners). There was a new study of the dangers of sweetners like Splenda just released, however I haven't seen it yet. If your soft drink gives you some kind of warning on it (you'll know because non diet sodas don't have this warning, and I wish I had a diet soda around to say what it is starts with a P though).
Mercury in vaccinations. I have seen news reports that say mercury is actually good for children.
Genetically engineered foods, these mainly consist of corn, soy, sugar and a few other crops. Very bad.
Monosodium glutamate (MSG). There is a reason you see "No MSG" on lots of packaging these days. Just search "MSG" in google and you'll relise how bad it is.
Late last year the FDA (same people that say Floride is good to drink) finnaly aproved that a certain amount of Melamine may be in baby formula, after they had concluded no level of Melamine was considered safe for consumption. Melamine had made 50k+ babies in china ill and killed many people. However it's ok to feed to your babies right?
Melamine traces found in samples of U.S. infant formula: Scientific American Blog
FDA sets 'safe' levels for melamine in baby formula - CNN.com
Tip of the ice -burg. This is how they are soft killing us.