C.G.
I'm not going to introduce dairy to mine at all, I have done tons of research and it is not good for kids, let alone young kids. It isn't even good for adults, there are plenty of other milks out there if milk is what you are after, there are a ton of options aside from soy too. My baby has had problems with soy from birth, but loves hemp milk, rice milk, hazelnut milk, etc.
Look up the effects of dairy and cows milk protein on the human body. The closest thing to human milk for the human body, that I have found, is goats milk, if supplementing is needed.