Because you can test the sparrows without having to raise an infant on the site. If you can demonstrate areas that are unsafe or illegal to raise children in, t

Because you can test the sparrows without having to raise an infant on the site. If you can demonstrate areas that are unsafe or illegal to raise children in, then perhaps people won't raise children there (or not, given we already know these mining towns are toxic and children raised in them will be victims of lead poisoning to various degrees). The reason they are testing children in the article is to confirm that the sparrow test is a valid proxy, and we will be able to test on a wider scale around the country.