Each is used when referring to individuals in a small, definite group of two or more. It correctly emphasizes that every single person in the group received a prize.

১. A few of the three is logically inconsistent because three is a specific number.
২. Every of is grammatically incorrect; every cannot be followed directly by of.
৩. All of the three boys would imply a collective action rather than individual.

অতিরিক্ত তথ্য: Each functions as both an adjective and a pronoun in English grammar.