According to the American Cancer Society (ACS), consuming food sources of soy (like tofu, soybeans, and soy milk) is safe for humans.
The ACS says the research in this area has been done in mice, and mice metabolize soy differently than humans. Studies in humans have not shown harm from eating soy-based foods. For young toddlers who drink soy milk, make sure to choose the whole milk versions that are fortified with calcium and vitamin D. Soy milk contains isoflavones (phytoestrogens), estrogen-like hormones that are also found in plants such as whole grains, apples, and potatoes. There is no evidence that the phytoestrogens in soy-based foods pose a risk for children.