3 weeks old baby can drink soy milk, but we should pay attention to the amount of soy milk should not be too much, soy milk is rich in protein, vitamins, etc., especially high-quality protein, rich in vitamin C, etc., for the immunity of the pediatric organism and growth and development have a very good role. However, soy milk is a food containing estrogen-like effects, which can regulate the level of estrogen in the body, which can lead to an increase in the level of hormones in the body, especially for female babies, if the long-term intake of soy milk in large doses, may lead to an increase in the level of estrogen in the body, which can cause early sexual development or precocious sexual maturity of female babies. So even though soya milk is rich in nutritional elements, but must pay attention to the amount of oral should not be too much, in daily life try to ensure a balanced and reasonable diet, try not to be partial, picky eaters, so as to facilitate growth and development.