I am not at that stage yet (actually I am still pregnant) but these are things that I am worrying and thinking and researching about too and I found that the multi-vit brand that I am taking (and that I really like) makes a supplement for infants 6 months & older. The brand is Rainbow Light and here is the link to the product. http://www.rainbowlight.com/product.aspx?id=TBD4&mid=1565
Let me know what you find out about exclusivly breastfed babies and the need for multi-vitamins.