It is true that milk is a good source of vitamin D and calcium. It helps prevent things like Rickets which was why it was mandatory in schools when I was young.
It is also one of the few non-sugary examples of a kids drink so I'm quite keen on it.
Milk has ~26g sugar per 16oz serving. It is about 33% less sugar than an equivalent coke, but that doesn't mean it is non-sugary or anywhere close (unless you meant non-sugary in terms of it doesn't taste very sweet, regardless of actual sugar content)
It is also one of the few non-sugary examples of a kids drink so I'm quite keen on it.
I liked it when I was young.