Based on the weight of the child (20 lbs), you can give them 4.2 ml of the children's Tylenol (160 mg/5 ml) every 4 to 6 hours if needed, with a maximum of 5 doses in 24 hours. This dosage has been calculated to be in line with the recommended 15 mg/kg per dose for children. Make sure to check the expiration date of the product before administering it to your child.