With the caveat that there is no support for "herbicides turn kids trans," I think it's important to understand what the science actually says so that we all have enough background information to have intelligent conversations with people who make these claims.
The most recent research on Atrazine was carried out by a Berkeley prof I know (and who is impeccable in his science). Basically it showed that exposure caused sex change and infertility in frogs via disruption of the endocrine system. Any disruption to the endocrine system can impact physiological sexualization, as it is exposure to the sex hormones during development that largely controls that sexualization.
Separately, other studies by different research groups have linked Atrazine exposure in the womb to developmental changes in humans. Our endocrine system is not drastically different than a frog's (to a large degree, most vertebrates are pretty damn similar).
Because exposure to the sex hormones during development controls physiological sexualization (it's largely a boost of testosterone controlled by several genes on the Y chromone that signals the embryo to develop as male, for example), and because that physiological sexualization includes differential development of the brain, it is not outside the realm of realistic possibility that exposure to certain chemicals during development that are known to impact the endocrine system can impact the physical sexualization of humans, including brain development, which would potentially have a large impact on subjective gender experience.
Again, THERE IS NO EVIDENCE THAT HERBICIDES TURN PEOPLE TRANS. But knowing this background I think is important if you happen to meet a conspiracy theorist who's done a bit more reading on the subject.