When taking vitamin C supplements, be careful not to exceed the NIH's recommended upper safe limit (an upper safe level has not been established for infants): 

• toddlers 1-3 years old -- 400 mg;
• children 4-8 years old -- 650 mg;
• children 9-13 years old -- 1,200 mg;
• teens 14-18 years old -- 1,800 mg; and
• adults -- 2,000 mg. 

The Dangers of Too Much Vitamin C 

Like everything, moderation is key. Vitamin C is a water-soluble vitamin excreted in the urine once the body has fulfilled its need. But too much of any substance, from vitamin C to water, can be harmful to health, so doctors caution only to use vitamin C supplements in moderation.