My daughter doesn't drink straight milk. Rarely has. I've made her a yogurt smoothie since she was 18 months. (Basically diluted yogurt: 3 yogurt cartons, 1/2 cup of milk--enough to make it liquidy, put thru a strainer to get the seeds and fruit chunks out. It helps if you have two big measuring cups to use, one to mix it up in, and one to pour into through the strainer. I now make smoothies for 2 days at a time: 5 cartons of yogurt and 3/4 cup to 1 cup of milk; it makes 4 cups according to my 4-cup pyrex glass measuring bowl; I pour 8 oz into four sippy cups.)
The recommended milk intake guidelines for over 12 months of age is no more than 16 oz of milk a day. She drinks two 8 oz cups a day (drinks it through a straw; likes to pick the straw color which makes it fun for her); one 8 oz cup in the morning with her cartoon (until age 4, this was her primary breakfast; she now asks for cereal also), the other 8 oz smoothie in the late afternoon (when we get home from daycare, sometimes another one if she's hungry before bed).
There are 5 oz of protein in each carton of yogurt... So, with 3 cartons she's getting at least 7.5 oz of milk-based protein each day, plus fiber and probiotics for her immunity. I think the smoothies are a main reason why she's never had constipation issues and is rarely ill with daycare viruses.
The homemade smoothies have an equal amount of protein as pediasure (pediasure has 7 oz), but no soy protein and no high fructose corn syrup (I personally choose to buy yogurt made with sugar instead of corn syrup).
Yes, there is sugar in yogurt but I don't add any additional sugar, honey, jam or flavorings to her yogurt smoothies; it was an intentional decision to gear her to like "normal food". On the few times she's said that she wasn't going to drink the smoothie, we turned the TV off... "Gotta drink the smoothie if you want the cartoon"... And that smoothie was gone.
For the rest of her meals, *she* prefers and requests water. (Juice was never a regular choice and she never became a big fan of it.)
I'm not a proponent of sweetening food in order to get a kid to eat it. There are other ways, you just have to approach it differently. My kid wouldn't drink milk, then I needed to try another form of dairy based protein--yogurt. Chocolate, strawberry and other sugar-based flavors added to milk (and which offer no other nutritional value) never entered my list of alternatives for my then 18 month old.
Good luck! (By the way, my daughter is allergic to cow's milk so her smoothies are made with goat milk and goat milk yogurt.)