In giving vitamins to your babies, please remember that there is a recommended dose for age related, and more than enough will cause harm.
For vitamin A, the recommended dosage for babies younger than 1 is 1500IU/day (IU means international units), from age 1-12, it is 2000IU, for >12 to adults, it is 5000IU.
Vitamin A is said to help vision and a lot of other metabolisms, and some even think it can help asthma. But too much of it will cause harm to the liver and bones. I don't know if anyone of you has seen news >1/2 year ago that a mother fed too much vitamin A to her 3 daughters to try cure asthma and they all got liver damage and nearly need transplant.
As for Vitamin C, I forgot the recommended dosage, but I know that many will think too much will just pass out in the urine and cause no harm. Quite contrary, too much will harm the kidneys.
For other vitamins they all have their recommended dosage for the children age group. You can find them on the FDA website or the WHO websites