I love the word παιδιά. It has a very gentle, kind sound. Perfect to mean 'child.'
Why is the article "the" needed in the translation? "Children drink milk" as a generic, can make perfect sense in English.
In general, the subject of the verb needs definite article in Greek. Παιδιά πίνουν γάλα is wrong.
But no one says"παιδιά πίνουν γάλα" . The nouns in greek always need an article