Three and a half year old children do not eat well is usually caused by zinc deficiency or bad eating habits, should be taken according to the situation of zinc, correct eating habits and other methods. 1. Zinc supplement: When children are deficient in zinc, they are prone to loss of taste, loss of appetite and other manifestations, according to the situation, you can eat some zinc-containing foods, such as beef, fish, shrimp, seaweed, etc., but also in the doctor or pharmacist under the guidance of the use of zinc supplementation medication, such as calcium and zinc gluconate oral solution and so on. 2. Correct eating habits: children eat too many snacks before meals, or picky eaters, etc., the performance of not eating well, parents should be carefully observed and patiently teach, urge children to form good eating habits, conducive to the growth and development of children. In addition to the above reasons, there are other factors that can lead to children not eating well, if necessary, parents can take their children to the hospital for professional diagnosis and treatment.