Recent studies showed that while oranges are an excellent source of vitamin C, the content of orange juices varies greatly, depending on the storage time. For instance, ready-to-drink juices average at 27 to 65 mg per cup at opening reduce to 0 to 25 mg per cup at expiration about 4 weeks later. It is therefore prudent to purchase ready-to-drink orange juices 3 to 4 weeks before expiration date and consume them within 1 week of opening.
An intake of a serving or two a day of the good sources (*) will easily meet your child's daily vitamin C requirements.