Translation:Milk is for both children and adults.
Is there a more succinct way to say the same thing in German? I'm just curious.
Sure, there are. The main thing is, the adjective/adverb is missing here. It works without and is very broad and general, but it sounds odd. Better example would be. Milch ist gut/geeignet/gesund/nahrhaft/.....fuer Kinder als auch fuer Erwachsene. This would be a normal German sentence where you determine what the milk is known to be good for.