General:
* കുഴലൻ കുട്ടി (kuzhalan kutti): This literally means "slender boy" and is a common way to describe a thin boy in a neutral way.
* ചെറിയ കുട്ടി (cheriyakutti): This means "small boy" and can be used to describe a thin boy, implying that he is small in stature.
More specific:
* കുറിയ കുട്ടി (kuriyakutti): This means "thin boy" and emphasizes the fact that he is thin.
* മെലിഞ്ഞ കുട്ടി (meliñña kutti): This means "lean boy" and is a more formal way of saying "thin boy".
To avoid any potential negativity:
* പാലു കുടിച്ച കുട്ടി (palu kutichcha kutti): This means "milk-drinking boy" and is a positive way to describe a thin boy, implying that he is healthy and well-nourished.
The best way to choose the right phrase is to consider the context and your intended meaning.