It is recommended by the NHS that adults need 40mg of vitamin C a day. They have set the safe limit as up to 1000mg a day of vitamin C, and this is commonly found in vitamin C supplements. Anything more than 1000mg is not recommended as it can cause stomach pain, diarrhoea and flatulence (4).
For children it is recommended by the department of health that all children aged 6 months to 5 years should take a vitamin C supplement containing vitamin C (ascorbic acid) (5). If the baby is formula fed then to double check what is provided vitamin C is provided in the formula milk and not to double dose with another supplement.