For a 12-month-old baby who is constipated, you can give them Lax-A-Day or a similar product that contains PEG-3350. The dosage is 1 gram of powder per kilogram of the child's weight, mixed in a small amount of any liquid and given once a day as needed. Be sure to follow the instructions on the product label, or consult with a pharmacist for assistance with measuring the correct dosage for your child.