The studies by Columbia University, the University of California at Berkeley, and Mt. Sinai Medical School measured commonly used pesticides in pregnant mothers.
It's the first to study their effect in utero and then, seven years later, to test their children's IQs.
They found that above average-exposure to the pesticides was linked to a drop in the children's IQs by as much as 7 points.
One scientist said he is concerned why the hazards weren't identified earlier, before several generations of children were exposed to the chemicals.
The pesticides in question are called organophosphates are found in a whole range of simple everyday products.
They are used for fruit and vegetable crops, and to control cockroaches in city apartments. They are also found in home weed killers. They've also been detected in the drinking water supplies of several American cities.
Some have since been banned but are still detected in the environment.
Scientists call this is another alert that more needs to be done to protect the most vulnerable beings from dangerous chemicals.
To reduce risk, pregnant women can wash food more thoroughly, and seal up their homes against insects, rather than relying on pesticides.
The studies were funded by the Environmental Protection Agency and the National Institute of Environmental Health Sciences.
