I don't understand the dosage for the prescription for my 2 and a half year old son who broke his arm yesterday.

You can bring the prescription to your pharmacist who will be able to fill it and explain everything to you. If you already have the products at home, you can give the correct dosage in either syrup or chewable tablets. It's usually easier to give a more precise dose with syrup. Acetaminophen comes in two concentrations, either 80mg/ml (for infants) or 160mg/5ml (for children 2 to 12 years old). For ibuprofen, there are also two concentrations available, 40mg/ml (for infants) or 100mg/5ml (for children 2 to 11 years old). Make sure to follow the correct dosage instructions for your child's age and condition.