Translation:Aloha, e ke keiki.
Is ke/ka used because the subject is a common noun? Would you also say "Aloha, e ka 'ilio"? I believe one would always address a teacher with "Aloha, e ke kumu."
Copying from link posted by PsilentPspeaking This is where the translation of "ka/ke/nå" as "the" breaks down. Polynesian languages don't have definite and indefinite articles the way most Indo-European languages do. What they DO have are "noun markers" which are used far more consistently than articles in Romance or Germanic languages. Nouns always need to be preceded by some kind of noun marker, as the distinction between "parts of speech" is far more fluid, so they're needed to contextualize that we're dealing with a noun, rather than a verb, and adjective, etc.
Where I lived in Hawaii no one spoke this way. I'll give examples. It was always simply "Aloha!" or "Aloha [Name]." It was implied who you were speaking to, whether an individual or a crowd. As kids we were simply called keiki. No gender separation and singular/plural was implied. These were easily understood be context so the extra markers etc. were usually unnecessary. I can't say my understanding of Hawaiian grammar is very advanced. My understanding is practical and of common everyday direct verbal interactions. The lessons here feel very formal, as if one needed to write a graduate thesis in Hawaiian. Perhaps this is regional. Anyone here have a similar or different experience?
There is always big difference between grammar and everyday use of the actual language. Goes for most languages. When learning a language (in my opinion) it is always good to learn the "proper" way (or formal like you said). The everyday way speaking will be easily learnt by using the language but having the grammar base will help avoid embarrassing situations should you ever need to speak professionally or showing respect (formal situations). I speak for experience as an Italian living abroad.