Best as I can tell so far (and no one really knows yet) autism is caused by injecting vaccines containing mercury (and/or other toxins) into infants at certain ages when certain parts of the brain are developing. There may be no "cure", but some claim to have reversed the problem by various means, including chelation therapy to remove heavy metals. But as far as we know, autistic children are no more or less sensitive to various "chemicals" than anyone else. It would not be good for anyone to have a drink of Trimec, but if you carefully spray trimec on some clover patches, this should have no way of affecting their child unless he goes out and eats some of the clover right after you spray it. All the herbicides are different, but most will be broken down within days or weeks of use. So you can solve the clover problem with $1.00 worth of chemical, or it could cost hundreds to use other means, such as removing and replacing soil or trying to gradually change the lawn. But of course it will be beneficial to treat the lawn well organically anyway. These people may be a pain. But you may be able to explain some options, and maybe they can be less picky and more patient. Corn gluten meal, is very high in nitrogen, so it might be good to treat with CGM, like lots of it, many times a year, and see if this helps with the clover. It is expensive, but it should be good for the lawn anyway. Might even prevent some annual weeds.