Milk should be the beverage of choice for growing kids who do not have contraindications. 3.25% milk is recommended up until 2 years of age, and to continue into older age if there are no issues with obesity.
I have my doubts about such recommendations; aside from the influence of the dairy lobby, how many such nutrition guidelines account for high-quality non-dairy alternative sources of protein and calcium?
The only dairy alternative that has comparable protein quality (DIAAS) is soy, and AFAIK there aren't many studies of soy milk given to toddlers/small kids.
Consumption of a mostly soy diet by small children is undesirable because of the presence of phytoestrogens in soy.
Pulses would come close second as a protein source, but a child would have to consistently eat larger servings in order to keep up with other meat-eating-and-milk-drinking children. Large portions are not always realistic in ensuring adequate protein intake in kids, who will occasionally go through phases of fussy eating.
Adopting vegetarian or vegan habits is great when periods of significant growth stop (and maybe this is what humans are meant to do, rather than to keep eating animal products in adulthood).
However, from my own experience, meat and milk is a necessity for avoiding malnourishment in little humans undergoing development.
I drink a ton of milk, maybe a third of a gallon a day. Always thought the obsession with counting calories was a little misplaced. It always seems to be very fit people drinking a ton of milk. People think that junk like Special K is healthy and great stuff like butter, eggs, and milk is bad for you. Tell that to French people who live to 120.