We were told by the doctor at age 1 for the twins the standard advice of starting whole milk. I was still nursing and was not planning on non-human milk, so to speak -- just food and water.
Anyway, he convinced me to do regular milk -- the girls have never been on the charts for weight, and while I had researched the milk v. no-milk issue, and have friends who don't give milk and who have very healthy kids, I decided to follow his advice. I did do some powdered goat milk, and also just the organic off-the-shelf stuff, etc.
At this point I wish I had just done no processed milk. When we moved here to Richmond and were able to find a local goat farm so we could get the fresh milk, I decided to do that. My feeling is that grass-fed milk (cow or goat) is nutrient-dense, and again because of their skinniness, I was willing to give them the local fresh stuff. That is a complete luxury as we are able to get it here in VA and the laws vary widely from state to state (go to http://www.realmilk.com
for more info). But what I learned in the process of doing that research was that even the organic milk I had been buying was not very nutritionally dense, that calcium is best procured from vegetable sources, that the homogenization process alters the fat cell structure of the milk and makes it less digestible (hence the milk allergies you see among children and adults which go away if they drink unhomogenized), and that pasteurization of course wipes out the enzymes that make milk in its true form a living food.
Your question addresses liquid v. powdered milk. My thought there is that the process of turning milk into powder via drying and grinding and treating it for anti-caking would only be worth it to me if I knew the cows were grass-fed -- i.e. that milk was nutritionally as it should be, as opposed to coming from grain-fed cows where their stomachs can't handle the grains properly (other animals like horses do fine on grain -- cows just don't).
I would do the research if I were you and see how you feel after reading about grass-fed v. feedlot-fed (I came to learn that a lot of organic milk is feedlot fed). If you are lucky enough to live in a place like California, you can buy fresh milk off the shelf. But if you don't have that ability, or the ability to get milk from a local farm or to buy grass-fed, but pasteurized milk at the store (we have a farm here in VA which pastures its cows, but they must pasteurize and homogonize -- I will still get that in a pinch as it is grass-fed).
But, I've been thinking a lot lately about processed food, and I think that each step a food takes away from its source can be considered processing. Powdered milk has been heat-treated, homogonized and thus altered at the structural level, subjected to a drying/grinding process, and then treated to make it storable and give it shelf life -- now, in this country there is a rich tradition of healthy farm kids growing up drinking milk, which the milk industry would very much like for you and I to believe that we tap into when we buy a carton of milk at the 7-11 -- but by the time you get the standard carton of milk or powdered milk, it has had its best nutritive properties stripped from it completely, and for many it has furthermore been altered into a substance which is indigestible in its ultra-processed form.
If I gave up my fresh milk, I'd switch instead to using high-quality fats and focus on buying fresh butter and other quality nutrient-dense foods, and local vegetables. The milk message in this country is about the dairy industry, not about our children's dietary needs for milk or that their bones need the calcium (on that front, you'll do your child a favor by cutting out fluoride, which stores in bones and causes brittle bones and teeth -- that is the single most important step a mother can take toward achieving excellent bone and teeth health for her children, aside from feeding healthy foods and avoiding sugars in general.
Well, as ever -- just my .02 which I did not intend to be this long! But I do feel like you don't have to even look at it as powdered v. liquid when the other questions are the most important ones -- milk v. no milk, and if "milk," then how do I get grassfed and as unprocessed as possible?