Baby/baby

Is it an actual human baby that's crying? then it would be 'baby.'

or is it a term of endearment, something you call your girlfriend? then it would be "Baby" because you're using it in place of her name.

A capital letter belongs at the start of a sentence or for a proper noun within the body of a sentence. A proper noun is the name of a place or person.

You are doing very well at English Yoong Liat.

If Baby is a nickname, a capital letter is appropriate. If baby it is a term of endearment a capital letter is not appropriate.

Sometimes substituting another similar word or rewording the sentence can assist in determining the correct manner of use.

Thanks. Happycat.

Thanks, Dadpad.

Stop wailing sweetheart. (using sweetheart as a substitute for baby intended as a term of endearment)

Stop wailing Happycat (substituting Baby intended as nickname with Happycat used as a nickname)

Thanks, Dadpad.

I got it.

Thank you.