The problem with juice (any juice) from our perspective is the concentrated nature of them (this outside of the preservatives, sugars, additives, etc.). If you've ever made your own juice you may know how much goes into a small glass. Some people who promote juicing consider this a good thing - "look how many vegetables/fruits/etc. I can stuff into this glass". From the bodies perspective this may be difficult to process. From our "common sense" perspective if you cannot eat that many vegetables/fruits at one time, you probably should be drinking that much.
Whole foods vs. anything processed, canned, packaged, etc. is always the way to go from a natural perspective. The whole "more is better" mentality is a largely western/american ideology that has little relationship to facts or common sense many times - but it does sell well.
As far as milk. Children should be breast fed first and foremost when they are young. The benefits of this are well documented, and again it makes sense naturally. As for children past the age of breast feeding, milk is almost a cultural issue more than it is anything backed by medical reasoning. Milk is recommended by many because it is nutritionally dense and contains calcium which is important for children and adults. There are plenty of other things, however, that contain calcium - some of the best sources are:
Spnach, Broccoli, Collard Greens, Tofu, Beans, Almonds, Apricots, Currants, Oranges, and more.
Milk is cultural in the sense that many cultures do not utilize it past a certain age if at all. The downside of milk is that it is generally hard for our bodies to digest and leads to an accumulation of dampness (in Chinese Medicine terms) in the body - this contributing to allergies, digestive problems, obesity, diabetes, etc. over the long run. Our bodies are built for breast milk not cow's milk. This argument, again, doesn't take into account the obvious downsides of the hormones and pasteurization issues.
So we do not recommend milk for children that are past the age of breastfeeding, certainly as a constant drink. Yogurts, cheeses, that are of high quality appear to have a less disruptive impact on the digestive system and are recommended in moderation so long as the child does not have allergies (to anything, not just to milk). If children have a largely whole foods diet with a broad range of foods there is a low probability that they will fall short on anything.