You don't really need to give them the vitamins unless there is a special reason to do so. Their starter has vitamins added to it already, I believe. Iron is one of those things that they should not overdose on. It has a cumulative effect, if I'm not mistaken. That's why folks that use the Red Cell supplement made for horses with their birds must be careful not to give too much or too often since it is iron-rich.
AviaCharge 2000 is a powdered vitamin/mineral/amino acid supplement especially for birds. You add to water on occasion. I use only the 1 gallon waterers since it turns the water a dark brown, like strong tea color, and stains the container a bit. You are supposed to only give it for I believe 48 hours, then remove it. I do it occasionally for my birds. It's quite expensive, though goes a very long way, and you can only order it online.