This is part of the overall issue of children' s particular susceptibility to chemicals in their environment. Since children crawl on carpets and put objects in their mouths, they get exposed to any contaminants that may settle onto those carpets or objects, including pesticides that were sprayed many days before. In addition, since children weigh less, they can't tolerate as big a dose of cough syrup, and certainly can't tolerate as big a dose of any toxic chemicals. We're almost there scientifically, but not quite. Laboratories at the National Center for Environmental Health in Atlanta have developed methods to test for a wide range of toxic chemicals in blood and urine.
Some commercial labs can test air or dust for a range of contaminants but, again, expensive.
The easiest thing to test is water. You should receive a 'report card' from your water utility at least once a year reporting on their testing results. If you haven't received anything from your water utility, call them up, or check their web site. I'm hoping that within the next five years or so, we will be able to test for a range of contaminants in the doctor's office, just as we can easily test blood lead levels today. That way we will have a better way of counseling individuals about their own exposures and risks.