I can remember babies being given vitamin drops a very long time ago, I mean forty five or more years ago. However most are eating proper food from six months. I didn't give mine any extra vits whilst feeding or when he was having 'dinners',etc. It probably wasn't so much the thing at that time and we were fortunate that he always had a healthy appetite with plenty of variety.
Can't do any harm though and there are some kids who aren't interested in food.