If your 3-year-old child has been constipated for 4 days, there are a few things you can do to help. First, try limiting their consumption of cow's milk, as this is a common cause of constipation at this age. Increase their intake of water and soluble fiber from fruits and vegetables. You can also visit a pharmacy to get a product called Lax-A-Day™, which can help things move along more quickly. Be sure to follow the dosage instructions based on your child's weight.